A randomised trial comparing the topical application of 1% fusidic acid with 0.3% gentamicin solution in the reduction of the normal preoperative lid and conjunctival microbial flora was performed. Forty patients awaiting cataract surgery were randomly divided into two groups consisting of 20 patients each. The first group received a 1% microcrystalline suspension of fusidic acid, the second 0.3% gentamicin to the preoperative eye every two hours between 0600 and 2400 daily for 48 hours preoperatively. Cultures were obtained from both the lid margins and the conjunctival sac of both groups prior to antibiotic therapy and again in the operating theatre before surgery. Microbiological identification and colony counts were performed by standard laboratory methods. Staphylococcus epidermidis was the commonest micro-organism isolated. Statistical analysis revealed no significant differences in the ability of a 1% microcrystalline suspension of fusidic acid and 0.3% gentamicin in eliminating or reducing the normal preoperative conjunctival or lid flora.