Cefixime is an orally absorbable cephalosporin with an extended spectrum of in vitro activity for gram-negative bacteria especially members of the Enterobacteriaceae. Gram-negative rod isolates collected over a three month period were tested against cefixime. Greater than 99% of Escherichia coli isolates was susceptible to cefixime including those resistant to ampicillin. Similarly isolates of Klebsiella, Proteus and Providencia were also exquisitely susceptible to cefixime as were 91 % of Enterobacter cloacae and 71 % of Enterobacter aerogenes. Killing kinetics of cefixime did not differ from that of the intravenously administered third-generation cephalosporin, cefotaxime. The addition of magnesium and calcium divalent cations or the lowering of the pH to 5.0 did not affect the action of this antibiotic. The extended spectrum of this oral antibiotic may be useful in treatment of urinary tract and skin and soft tissue infections caused by the more resistant gram-negative rods.