The aim of this study was to examine the in vitro activity of fusidic acid against bacterial isolates from conjunctival swabs. Conjunctival swabs from 213 patients with conjunctivitis were examined. One or more pathogens were grown from 73 patients. Forty per cent of isolates were resistant to fusidic acid on disc sensitivity testing. Reduced sensitivity was detected by minimum inhibitory concentration testing in many isolates of H. influenzae and an isolate of S. pneumoniae. In addition, the in vitro activity of fusidic acid was determined against upper respiratory tract isolates of H. influenzae, S. pneumoniae and M. catarrhalis; this showed that many isolates had a reduced sensitivity to fusidic acid. Topical fusidic acid may not be optimal empiric therapy of bacterial conjunctivitis.