In order to study the distribution of bacteria in the operating room environment, cultures were obtained during 111 unselected shunt operations throughout a 10-month period. After routine skin preparation, bacteria were collected by placing Millipore filters on the patient's prepped skin underneath the drapes, on top of the drapes in the operative field, and/or on the sterile instrument table, and left in place for the duration of the case. In 48 patients, full-thickness skin biopsies taken at the initial incision were cultured in lieu of skin surface cultures. Perioperative cerebrospinal fluid cultures and subsequent shunt infections were monitored. Of the 288 environmental (skin and surfaces) cultures, 24 were positive (20 coagulase-negative Staphylococcus and 4 Staphylococcus aureus). Positive cultures were found in 15 of 111 drape cultures (13.5%), 7 of 77 instrument table cultures (9.1%), and 2 of 97 skin cultures (2.1%). Positive environmental cultures were not correlated with the surgeon, length of case, time of day, or type of shunt operation, but were more likely to occur in a room other than the designated neurosurgical operating room. There was a correlation between the occurrence of positive environmental cultures and positive cerebrospinal fluid cultures, although the organisms were not always the same. Coagulase-negative Staphylococcus was the most common organism isolated from all sites. We conclude that bacteria most often associated with shunt infections are airborne in the operating room, rather than originating from the patient's skin, and are distributed in the highest concentration near the surgical team.(ABSTRACT TRUNCATED AT 250 WORDS)