A new blood lysis-filtration culture technique revealed a high incidence of Staphylococcus epidermidis in the blood of patients and of healthy people. Of 2,004 blood cultures from patients, the blood lysis method grew S. epidermidis in 233 (11.6%), whereas a conventional two-bottle culture system grew this organism in 48 (2.4%). To determine the incidence deriving from the skin, 100 mock blood cultures by each technique were performed. The antecubital fossa was prepared as for a phlebotomy. The needle was inserted through the skin but not into the vein. Needles were cultured by conventional and lysis-filtration culture. A total of 1 conventional culture of 100 (1%) and 2 lysis-filtration cultures of 100 (2%) grew S. epidermidis. Of 100 lysis-filtration and conventional control cultures with broth in place of blood, no cultures were positive. Blood samples from 8 of 117 (6.8%) healthy blood donors were positive for S. epidermidis by lysis-filtration, whereas no matching conventional cultures were positive. Phage typing patterns of skin and blood strains from selected individuals were the same. S. epidermidis isolates were often concomitant with isolates of bona fide pathogens. I conclude that intermittent, transient, asymptomatic S. epidermidis bacteremia occurs frequently in patients and in healthy humans.