The Japan Adult Leukemia Study Group analyzed infectious episodes in 577 patients with acute myeloid leukemia during remission induction therapy between 1987 and 1991. 542 patients (93.9%) experienced at least one infectious episode, 121 (21.0%) had microbiologically documented infection; there was clinically documented infection in 184 (31.9%) and unexplained fever in 237 (41.1%). Among 121 microbiologically documented infections, bacteremia/fungemia was observed in 68, pneumonia in 33, and other types of infections in 20. Among the bacteremia/fungemia, gram-negative bacteria accounted for 41.2% (Pseudomonas aeruginosa was the most common), gram-positive bacteria for 39.7%, fungi for 16.2% (Candida spp. being most frequent), and polymicrobial for 2.9%. The most frequent isolates among pneumonia were Pseudomonas aeruginosa and Aspergillus. A total of 70 patients (12.1%) died during remission induction. Mortality of 68 patients with bacteremia/fungemia was 26.5%; in these patients, mortality with concomitant pneumonia increased to 41.4%; without pneumonia, mortality was 15.4% (P < 0.05). Mortality according to the isolated microbes was 17.2% for gram-negative bacteria, 25% for gram-positive bacteria, and 54.5% for fungi. Mortality of 113 patients with pneumonia (33 microbiologically documented and 80 clinically documented), 20 with other microbiologically documented infections, 104 with other clinically documented infections, and 237 with unexplained fever was 25.7%, 5.0%, 5.8%, and 5.1%, respectively.