John Greene thought he worked for a pretty good company. Then, at 40, he got cancer — and found out for sure.

In November 2010, after he’d been in Salesforce (CRM) engineering R&D for barely a year, Greene was diagnosed with acute myeloid leukemia. Married and the father of two young children, he started a blog from his hospital bed called “jg will kick its ass.” He posted about day after day of chemotherapy, kidney function, and the view of San Francisco from his window. And he managed to keep a sense of humor. “I think I’m going to donate quite a bit more to cancer research now,” he wrote.

Initially Greene shared details of his illness only with his boss and his small team. But his best shot was a bone marrow transplant, and he decided to send a systemwide message at work. “Within five minutes, [CEO] Marc Benioff called me,” Greene recalls. “I was in touch with him throughout. He even made sure I got the right medical care at UCSF.”

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Colleagues used Chatter — Salesforce’s internal ubiquitous social-networking app — to look for bone marrow donors. And late one night, Benioff tweeted, “Salesforce employee John Greene has AM L and needs a bone marrow transplant to survive. Are you a match?” By morning, 350 Salesforcians had signed up with the match registry. Salesforce covered insurance costs that Greene would have had to pay for himself. Its foundation made a $25,000 grant to the marrow registry in Greene’s name.

The story isn’t exceptional at Salesforce. Last month a 43-year-old British employee, Gillian Jenkins, found out insurance wouldn’t cover a new antibody drug for her Hodgkin’s lymphoma. Salesforce picked up the $54,000 tab. Benioff wrote her that if treatment would be better at UCSF, she could come to the U.S., and “we’ll take care of the costs for housing and treatment.”

Greene, who once worked for Phish doing software development and these days plays Grateful Dead songs once a week at his kids’ preschool, is back at work. He had a successful transplant (though in the end not from a colleague) and is doing well. “The company was awesome,” Greene says. If he didn’t know that already, he can ask his mother, Adrienne, back in Philly. Whenever he’s gone to work for a public company, Greene says, she buys stock in it and also checks out “who’s running the ship.” Lately, she’s been rather impressed.

This article is from the February 6, 2012 issue of Fortune.

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