Of 2160 intensive care unit patients, 36 patients with positive blood cultures had coagulase-negative staphylococcus in one blood bottle, whereas the organism was present in two or more bottles in 38 cases. The groups were not significantly different in 27 clinical variables, obtained at the time of their first positive blood culture. There was also no significant difference in the antimicrobial sensitivities. No initial clinical data supported the classification of coagulase-negative staphylococcus as either pathogen or contaminant. When the 74 patients with blood culture positive coagulase-negative staphylococcus were compared with three "control groups" ("absent septicemia," "probable septicemia" and "proven septicemia") they were not different from those with "probable septicemia." A discriminant analysis was performed comparing patients with "absent septicemia" and with "proven septicemia" in an attempt to classify patients with isolates of coagulase-negative staphylococcus in one of these groups at an early stage. Patients with two or more positive blood cultures were not statistically classified more frequently as septicemic than patients with one blood bottle positive for this organism. However, patients categorized as septicemic had a significantly higher mortality (59%) than those classified as non-septicemic (35%) (p less than 0.05).