Insusceptibility levels of cefaclor and other commonly prescribed antibiotics were determined for 489 consecutive hospital and community-associated urinary tract isolates of Escherichia coli from the Nottingham area of the UK. Significant resistance (MIC of > or = 8 mg/L) to cefaclor was found to be uncommon in the UK, with insusceptibility percentages as low as 1.5% and 1.4% amongst hospital and community isolates, respectively. When compared with other antimicrobials used commonly for treating urinary tract infection, only ciprofloxacin showed greater activity, though cefaclor showed significantly greater in-vitro activity than cephalexin, ampicillin and trimethoprim. Only seven isolates were insusceptible to cefaclor at a concentration of 8 mg/L. Each of these isolates produced a beta-lactamase, but it is unlikely that beta-lactamase production was the sole reason for insusceptibility since these isolates were also insusceptible to co-amoxiclav. Cefaclor compared extremely well with co-amoxiclav against ampicillin-insusceptible isolates, with none of the pharmacokinetic difficulties and considerations associated with the use of beta-lactam:beta-lactamase inhibitor combinations. Cefaclor appears to be a useful cost-effective alternative to current therapeutic options, particularly for long-term low-dose treatment of recurrent urinary tract infection in those geographical areas where the likelihood of resistance to other possible agents is becoming unacceptably high.