328 clinical isolates ofAcinetobacter calcoaceticusfrom hospitalized patients and persons attending general practitioners were characterized according to biotype and resistance‐pattern. 117 strains of biotype (b.) anitratus, 200 of b.lwoffi, 11 of b. haemolyticus and no strains of b. alcaligenes were found. B. anitratus was more frequently isolated from patients in hospitals than b.lwoffi; b.lwoffi was more often found in general practice. Strains of b.anitratus had more resistance traits than b.lwoffi. Strains of b.anitratus obtained in hospitals were more resistant than strains from general practice. No such difference was found with b.lwoff