Systematic collection of data on every Enterobacteriaceae clinical isolate cultured in the Central Bacteriology Laboratory allowed comparison of the percentage of cefotaxim (CTX) and moxalactam ( MOX ) intermediate or resistant (IR) strains among the 8 199 Enterobacteriaceae isolated in 1982 and the 5 032 Enterobacteriaceae isolated in 1980. In 1982, IR rates were 2% to CTX and 0.6% to MOX . Among the 166 strains IR to CTX, 28% were also IR to MOX . Two strains only were IR to MOX but not to CTX. No E. coli, P. mirabilis or Klebsiella strains IR to CTX or MOX were isolated. On the opposite, percentages of strains IR to CTX or MOX were respectively 2.5 and 0 for indole positive Proteus, 6 and 3.6 for Enterobacter, 7.4 and 0.5 for Serratia and 17.2 and 2.5 for Citrobacter. Strains IR to CTX or MOX represented 3.3%, 2.5% and 1% of Enterobacteriaceae isolated from pus, urine and blood cultures, and 4.7%, 2.2% and 1.3% of those isolated in urology, surgery and medicine. Between 1980 and 1982, there was a simultaneous increase in the consumption of CTX and MOX (10 fold) and in the percentage of Enterobacteriaceae IR to CTX (2 fold); this last involved Serratia (9 fold) more than Citrobacter (3 fold) and spared Enterobacter.