One hundred one nosocomial septicemias (NS) were studied among 461 cases of septicemias (22%) collected by French Septicemia Expert System Group during 1985. The mean-age of the patients was 58 +/- 23 years while it was 56 +/- 23 years in the 360 community acquired septicemias (CAS). The source of septicemia was found more frequently in NS than in CAS (79/101 versus 223/360; p less than 0.002): mainly urinary tract and intravenous therapy in NS, urinary tract, gastrointestinal and biliary origin in CAS. Invasive procedures (except surgical procedures) were more frequent in NS than in CAS (13/101 vs 14/360; p less than 0.0001). Underlying diseases were more often associated with NS than with CAS (96/101 vs 276/360; p less than 0.0001). Many pathogens were involved in these NS but the frequency of S. aureus meti-S and meti-R, S. epidermidis, Enterobacter, Klebsiella, Serratia, Proteus indol + and Pseudomonas carbeni-R was significantly greater in NS than in CAS. There was no significant difference between NS and CAS for septic localizations, respiratory distress syndrome and septic shock. Two antibiotics (and possibly 3 antibiotics for polymicrobial septicemias) were more often used in NS than in CAS (61/101 vs 135/360; p = 0.002). If the duration of hospitalization was not significantly greater in NS than in CAS (26 +/- 29 days vs 23 +/- 33 days), the overall mortality was significantly more important (25.6% vs 14.9%; p less than 0.05).