This study of 170 strains of Klebsiella-Enterobacter isolated at Boston City Hospital in 1967 confirmed most but not all observations made in 1963-1964 on the bacteriologic and epidemiologic characteristics and antibiotic susceptibility of this group of organisms. Klebsiella type 24 remained endemic and the most frequent serotype, but in 1967 type 2 strains were almost as frequent. Most type 24 strains were isolated from patients in surgical wards; patients with type 2 were more widely scattered. Both were frequently associated with instrumentation (mostly urinary catheters). Type 26 was endemic to the nurseries. Kanamycin sulfate resistance was more frequent in 1967, but two thirds of the strains were still sensitive. Resistance to polymyxin B sulfate was similar in the two studies. Nearly all strains were highly sensitive to gentamicin sulfate.