Google is to integrate its popular e-mail service with instant messaging, allowing users to chat and send e-mails from the same web browser window.
Google's Gmail service has grown steadily since 2004
The company hopes the new feature, known as Gmail Chat, will attract users by offering instant messaging without having to use a separate program.
Google's existing chat service lags behind rivals AOL, Yahoo and Microsoft.
The new facility will be visible to existing subscribers from within Google's Gmail browser window.
People will only be able to start conversations with fellow Gmail account holders, or those contacts using services compatible with Google's messaging facilities.
They include US-based Earthlink, the Jabber.org network and e-mail providers in the Philippines, China and Italy.
Some Gmail subscribers would begin to see the changes instantly as the service was rolled out on 7 February, the company said.
They include a Quick Contacts list that displays the contact the user communicates with most often.
The new service offers messaging services within a dedicated portion of the Gmail browser window.
Conversations can also be archived, although this feature can be turned off.
All subscribers would be able to use Gmail Chat within two to three weeks, the company said.
"We are breaking down some of the artificial barriers between e-mail and web browsing," said Salar Kamangar, a Google vice-president.
"We observed by talking with our users that there is no reason to think of IM [instant messaging] as different from an e-mail message."
Analysts suggested the move is designed to steer Gmail users towards the company's six-month-old Google Talk service.
Google Talk enables Google account holders to hold voice conversations using the internet on any machine equipped with a microphone and speakers.
AOL: 53 million
MSN: 27 million
Yahoo: 22 million
It also currently serves as Google's main instant messaging client.
"This is training wheels for Google Talk. It is a way to introduce a broader population to instant messaging and give them exposure to Google Talk," Greg Sterling of Kelsey Group told the Reuters news agency.
Gmail was launched in 2004 and is still technically at an experimental beta stage.
However, users are now allowed to invite an almost unlimited number of people to join the service, which generates cash by targeting advertising to the individual user.