Of 585 bacteremic episodes studied prospectively at Rokach Hospital during a 4-year period (1980-1983), 70 (12%) episodes observed in 67 patients were due to multiple species. A total of 170 strains of microorganisms were involved, 2-5 per bacteremic episode: 130 (76%) were aerobic Gram-negative bacilli, 36 (21%) were Gram-positive cocci (most of them streptococci) and 4 isolates (2%) were Candida. The most common sources of infection were the urinary tract (31 episodes), intra-abdominal foci (22 episodes, half of them from biliary tract), and skin or soft tissue infection (14 episodes). At least one organism was also recovered from a local focus of infection in more than 50% of cases. Many patients had severe underlying diseases in addition to old age. People with biliary infection had, however, a relatively lower frequency of underlying disease. Fifty-six percent of the episodes were hospital-acquired, primarily those related to urinary infection with indwelling catheters, intra-abdominal abscess and infected burns. Twenty-eight patients (42%) died as a result of the bacteremia. Polymicrobial bacteremia was found to be quite common in the population studied, and the urinary tract was the most important portal of entry, especially in the older patients.