The incidence of resistance of Gram-negative bacteria to three generations of cephalosporins was surveyed in two large hospitals with widely differing rates of cephalosporin usage. Overall resistance (MIC greater than 5 mg/l) of Enterobacteriaceae to cefotaxime in the hospital using large amounts of cephalosporins was 4% compared with 0.7% in the other. Enterobacter species accounted for most resistant isolates and resistant Enterobacter cloacae replaced sensitive strains in four patients given cefotaxime in 1983. The distribution of species colonizing intensive care areas was similar in both hospitals with cephalosporin-resistant Pseudomonas aeruginosa and Acinetobacter calcoaceticus predominating.