The in-vitro activity of cefdinir (Cl-983, FK482), an orally absorbed aminothiazole cephalosporin, was compared with that of penicillin, ampicillin, amoxycillin, amoxycillin/clavulanic acid (2/1), cefaclor, cefuroxime, cefixime, cefotaxime, vancomycin and erythromycin against 370 clinical isolates of Gram-negative and Gram-positive bacteria. Cefdinir was highly active against Staphylococcus aureus and S. epidermidis, inhibiting 90% of the strains at doses of 0.25 and 0.5 mg/l respectively. However, cefdinir was not active against methicillin-resistant S. aureus (range 16- > 128 mg/l). The respiratory pathogens Moraxella catarrhalis, Streptococcus pneumoniae, and S. pyogenes were also susceptible (MIC90 < or = 0.5 mg/l), but against Enterococcus spp. cefdinir displayed no useful activity. The common members of the family Enterobacteriaceae were susceptible (MIC90 < or = 1 mg/l), but those possessing chromosomal beta-lactamases were more resistant (MIC90 2-8 mg/l). The presence of human serum had little effect on MICs of cefdinir. These results indicate that cefdinir exhibited a wide spectrum for an oral cephalosporin and support its possible clinical use against susceptible pathogens in infections of the skin, soft tissue, respiratory and urinary tracts.