Minimal inhibitory concentrations (MICs) of seven cephalosporins: cefotaxime (CTX), ceftriaxone (CRO), ceftazidime (CAZ), latamoxef (MOX), cefoxitin (FOX), cefotetan (CTT) and CM 40876 (CM), of aztreonam (ATM) and imipenem (IPM) were evaluated by agar dilution with and without 5 mg/l of clavulanic acid (AC) or sulbactam (SB) for 28 strains isolated in 1986 (15 K. pneumoniae, 3. K. oxytoca, 4 E. coli, 4 E. cloacae, 1 E. aerogenes and 1 C. freundii). Comparatively to MICs of sensitive strains and to those of cured variants, MICs of these strains were very increased for CTX, CRO, ATM (mode MIC: 1 mg/l), and CAZ (2); weakly increased for MOX and CTT (0.25), and identical for IMP (0.12-0.25), CM (0.06) and FOX (2-4), except for Enterobacter and Citrobacter (64). Association with AC or SB did not modify MICs of FOX, CM and IMP. For the other antibiotics, MICs were reduced by addition of AC: Klebsiella: 5 log2 for CTX and CRO, 4 for CAZ and ATM, 2 for MOX and CTT; E. coli: 4 log2 for CTX and ATM, 3 for CRO and CAZ, 1 for MOX and CTT; Enterobacter and Citrobacter 2 log2 for CTX, CRO, CAZ and ATM, 1 for MOX and CTT. With SB, decrease of MICs was two to for fold lesser than with AC. AC, and less efficiently SB, restored activity of CTX, CRO, CAZ and ATM on CTX-1 producing Enterobacteriaceae, particularly Klebsiella and E. coli. It was the same for MOX and CTT, weakly affected by this resistance. AC and SB had not effect on FOX, CM and IPM which remained active on these strains.