Microsoft Corp. on Wednesday began selling the newest version of its Office suite of software, in a test of whether one of its most profitable businesses can continue to thrive in the face of a cheap online alternative from Google Inc.

Office 2010, which the Redmond, Wash., company made available for business customers, adds Web-friendly features to a collection of software products that accounted for nearly 60% of Microsoft's operating profit during its last fiscal year.

The new release includes versions of the Word, Excel and other Office applications that run inside Web browsers without having to install the programs on their machines, and allows people to edit documents in collaboration with other users.

The heart of Office, though, remains applications that companies will install on their personal computers, like the new Outlook email program that taps into information from Facebook and other social networks to give users a glimmer of what their email correspondents are up to online.

The new products are Microsoft's attempt to bring Office into the era of 'cloud computing,' a trend promoted by Google and others away from traditional software installed on PCs in favor of applications run entirely through Web browsers.

In a blog post Tuesday, Google seized on Office 2010's release to pitch business customers on the benefits of its competing suite of applications, called Google Docs. In the post, Google executive Matthew Glotzbach said Google Docs is a 'refreshing alternative to the expensive and laborious upgrades to which IT professionals have become accustomed.'

The Mountain View, Calif., Internet company charges business customers $50 per user a year for Google Docs and says it eliminates administrative hassles since Google runs all of the software in their data centers.

Stephen Elop, Microsoft business division president, said in an interview that he is confident Microsoft's offerings are more appealing to businesses than Google's.

'They have a lot of noise out there as it relates to their point of view, but when you look at the data and talk to customers, there's no question Microsoft is winning the customers,' Mr. Elop said.

Mr. Elop said 8.6 million people are already using Office 2010 and related products as part of Microsoft's largest-ever testing program.

The cost of purchasing Office 2010 can vary from under $100 to several hundred dollars per user, and can require additional purchases of software to enable collaboration on documents between business users.

Microsoft is giving away a free Web version of Office for consumers that will contain advertisements and omit many capabilities, though it expects most business customers will prefer more advanced paid versions of the product.