Poor patient adherence reduces the effectiveness of fecal occult blood testing for colon cancer. Patients at the inner-city clinic involved in the study have historically completed only one-third of the tests administered to them. The authors studied three ways of returning test kits (by hand, by mail, and by mail with prepaid postage). Among 146 randomly assigned patients, the completion rates were 37%, 57%, and 71%, respectively. The difference was significant between the first and third groups (p = 0.003), and the cost was less for the third group ($1.71 vs $2.24 per completed test). The authors recommend that clinics serving indigent populations use postage-paid return envelopes with fecal occult blood testing to improve its effectiveness and save money.