A randomized controlled study was conducted to compare effects of imipenem (IPM) (1.0-1.5 g/day) with those of aztreonam (AZT) (4 g/day) +lincomycin (LCM) (1,200-2,400 mg/day) in patients with malignant tumors or hematological diseases and severe infections. A total of 95 patients entered the study between October 1989 and March 1991. Forty-seven patients were treated with IPM and the remaining 48 patients were given AZT+LCM. No statistically significant differences existed in age, sex or underlying diseases between the 2 groups. Overall, the clinical cure rate of the IPM group was 53%; This was significantly higher than the 31% cure rate obtained in the AZT+LCM group (P less than 0.05). The difference was significant in patients whose granulocyte counts were less than 1,000/microliters, but not in those whose granulocyte counts were 1,000/microliters or higher. Side effects were observed in 5 patients given IPM and one given AZT+LCM. In conclusion, no significant differences appeared to exist regarding clinical efficacy and safety between the 2 treatment regimens.