Imagine not being able to use a mouse to open a Web browser or a keyboard to type an e-mail. What if you couldn't distinguish colors on a computer screen or type the distorted letters in order to buy concert tickets or enroll in a class?

Despite technological advances aimed at making the Internet easy to use, the World Wide Web is not wide open for many people.

But as the number of people with disabilities grows and more of everything is done online, companies are finding it makes good business sense to make their sites more accessible and are hiring consultants and training programmers to make it happen.

"Web sites are nowadays the virtual front door of a business. If you can't get in, you can't get your business done and they just lost a customer," said Dmitri Belser, the executive director of the Center for Accessible Technology in Berkeley, which has worked with Intel Corp., Gap Inc. and others.

There are more than 50 million people in the U.S. with disabilities, including blindness, hearing-impairments, mobility difficulties and cognitive and neurological problems.

The World Wide Web Consortium, which develops standards for the Web, has issued guidelines for designers to help them create more accessible sites. They include providing text labels for images, captions on audio and video and making keyboard shortcuts for people who can't use a mouse.

"When the Web is designed well, it is so enabling. It allows people to contribute on an equal plane," said Shawn Lawton Henry, outreach coordinator at the consortium's Web Accessibility Initiative.

While most federal government Web sites are required by law to be accessible, companies have no legal obligation to incorporate the features.

But Jim Thatcher, who developed the IBM screen reader, which blind people use to read the Internet, said the threat of civil rights lawsuits has motivated some companies.

Last year, Target Corp. agreed to pay $6 million in damages to plaintiffs in a California class action lawsuit who were unable to use its Web site. Thatcher, who was an expert witness during the trial, said there were many links on Target's site that were unintelligible to screen-reading software. He said there have been improvements since the settlement with the National Federation of the Blind.

Apple Inc. also reached an agreement with the state of Massachusetts to alter the program iTunes to make it accessible to the blind.

"No question that companies are seeking more help since those cases," said Thatcher, who is working with Amazon.com on its site.

Apple's iPhone has been praised for its accessibility features, including screen reader audio that comes standard on the machine.