The in-vitro activity of cefpodoxime was studied in 529 clinical isolates and compared with the activity of other oral beta-lactams. Amongst the Enterobacteriaceae cefpodoxime was very active (MIC90 less than or equal to 1 mg/l--other than genera commonly possessing chromosomal beta-lactamases). Against these strains cefpodoxime was comparable in activity to cefixime and about eight-fold more active than cefuroxime and 8-16-fold more active than cefaclor and cephalexin. Staphylococcus aureus strains were moderately susceptible (MIC90 4 mg/l) to cefpodoxime in comparison with cefixime (16 mg/l). The respiratory pathogens, Haemophilus influenzae, Streptococcus pneumoniae and Branhamella catarrhalis were susceptible to less than or equal to 0.5 mg/l cefpodoxime. An increase in inoculum from 10(4) to 10(6) cfu had little effect upon activity. Studies in beta-lactamase hydrolysis of cefpodoxime showed it to be stable to TEM-1, SHV-1 and BRO-1 enzymes but with high affinity for the P99 enzyme. The primary target of cefpodoxime is PBP3 (I50 1 mg/l) in Escherichia coli K12. The protein binding of the agent to human serum was 14.3-18.3% at 1 and 5 mg/l respectively.