Crest, a division of Procter & Gamble, is asking people to go to the Web to vote for their favorite from a short list of contenders: lemon ice, sweet berry punch or tropica exotica. Samples of the flavors are attached to some Crest products.

Marketing executives say the campaign reflects an increasing interest by companies in involving consumers in their advertising. The trend is another way to break from traditional advertising that viewers increasingly can tune out with TiVo and other digital video recorders. Marketers say the Internet has also made interactive campaigns easier to conduct.

"This comes with the inherent declining power of traditional media advertising," said Clive Chajet, chairman of Chajet Consultancy, a brand consulting firm in New York. "All marketers today are seeking different ways to market their products." Crest is running television and magazine advertisements about the promotion, which were created by Saatchi & Saatchi, part of Publicis Groupe. It also is sending e-mail to four million consumers on the company's e-mail list. Voters must go to Crest.com to register and vote. Then, they receive an e-mail message from Crest urging them to vote every day.

Similarly, Staples Inc. is starting its Staples Invention Quest vote Aug. 10. Staples accepted product ideas from customers this spring and said it would award a $25,000 grand prize in September and nine semifinalist prizes of $5,000 - along with possible production deals - for the best inventions, chosen by Staples judges and online voters.

Since the Crest voting began May 2, about 500,000 votes have been cast, said Tonia Elrod, a Crest spokeswoman. Staples, based in Framingham, Mass., received about 12,000 invention proposals this year, up from about 8,300 last year, said Jevin S. Eagle, the senior vice president of Staples Brands. Results for the contests at both Crest and Staples will be released in early September, and both companies will begin marketing pushes.

Crest and Staples have another advertising tactic in common: both introduced products last year on the NBC show "The Apprentice." Crest introduced its vanilla mint whitening expressions flavor last fall during the show, and Staples executives appeared on an episode in April to judge the inventions of contestants. Staples had the winning invention - the desk apprentice, a desktop storage container for office supplies - on store shelves the day after the show appeared. Staples also featured a video game about the desk apprentice on its Web site.

Procter & Gamble has run Web promotions for several other brands as well. For instance, Secret's Secret Sparkle deodorant line features downloadable instant message icons to decorate consumers' screens and a Secret Sparkle buddy option, which sends users beauty tips, games and quizzes when they log on their instant messenger screens.

The campaign for Secret Sparkle's newly released body spray features a Web log that includes postings by four fictitious characters that represent each body spray scent. Visitors to the site can also post messages there.

CoverGirl, a line of cosmetics also owned by Procter & Gamble, runs a Web site where people can ask beauty questions and receive immediate answers.

But does interactive marketing increase sales?

Executives at Crayola crayons, a product of the Binney & Smith subsidiary of Hallmark Cards, said sales increased when they held contests to name crayon colors, though they would not say by how much.

"If you took the time to submit a name because you really wanted to win this honor, you had to have some kind of connection or like for that color in the first place," said a Crayola spokeswoman, Stacy Gabrielle. The newly named crayons "become a collector's item; people really want them."

Crayola's first naming contest, in 1993, drew two million entries. But subsequent contests attracted fewer entries. Last year, a Crayola naming contest had 25,000 submissions.

Mr. Eagle of Staples said that the desk apprentice sold out after appearing on the show.

When consumers vote overwhelmingly for a product or participate in its development, it is more likely the new item will sell well, said Michael D'Esopo, a senior partner at Lippincott Mercer, a design and brand identity firm that is a division of Mercer Inc.

A study at the Yale Center for Customer Insights found that people who are told that a product is popular will buy it over a competing product, said Ravi Dhar, a professor of marketing at the Yale School of Management and a director of the center.

"Customers say, 'Hey, if everyone liked it, it must be good,' " Mr. Dhar said. "It shifts people's preferences."

Mr. Dhar said interactive marketing helps companies identify the consumers who care about their products and are most likely to buy them. Making that connection has been a challenge for companies that manufacture products and sell them through retailers rather than directly to consumers, he said.

Crest has tried to broaden that connection with a site and e-mail service called Crest dental plan, which offers dental health information and Crest promotions. Those who vote in the Crest contest are asked if they want to join the e-mail list, which will continue to poll consumers on their preferences, said Matt Barresi, Crest's associate marketing director.

In late June, about halfway through Crest's voting period, word is that lemon ice is in the lead. What if the other two catch up? "I guess mathematically it is possible there could be three winners," Mr. Barresi said. If it's close, "we could launch the favorite in September, and the others later in the fall."