At our institution, 95 cases of Acinetobacter septicemia occurred over a ten-year period (1973 to 1982) in patients being treated for cancer. In 24 patients the infection was polymicrobial, while Acinetobacter ssp was the only offending pathogen in 71 patients. In 76 patients (80%), the infection was related to an indwelling central venous catheter (CVC). A sharp increase in the frequency of Acinetobacter septicemia was noticed in the years 1981 and 1982 and coincided with a marked increase in the number of indwelling CVCs in use. Acute leukemia and breast cancer were the malignancies most commonly associated with Acinetobacter septicemia. The isolates of Acinetobacter calcoaceticus from the patients in this study were highly susceptible to the aminoglycosides and moderately susceptible to trimethoprim-sulfamethoxazole (TMP-SMX), carbenicillin, and tetracycline. Seventy-nine patients recovered from their infection with removal of the CVC and antimicrobial chemotherapy. Acinetobacter sp was the cause of death in none of the 16 patients who died. A calcoaceticus is an important nosocomial pathogen causing infections predominantly in immune compromised patients and frequently associated with indwelling catheters.