Mupirocin (pseudomonic acid A) is a novel topical antibacterial agent which inhibits bacterial protein and RNA synthesis. It has excellent in vitro activity against staphylococci and most streptococci, but has less activity against other Gram-positive and most Gram-negative bacteria. Its rapid systemic metabolism means it will only be used topically which, combined with its novel chemical structure, should make cross-resistance less likely to occur than with other currently available topical antibacterial agents. Mupirocin 2% ointment administered 2 or 3 times daily has shown excellent efficacy in both primary and secondary superficial skin infections, usually with at least 80% of patients being clinically cured or markedly improved, and over 90% eradication of the bacterial pathogen involved. Efficacy in impetigo and, to a somewhat lesser extent, infected wounds has been particularly convincingly demonstrated, while in other secondary skin infections the clinical response seen with mupirocin was often similar to the high success rate of vehicle alone. Limited evidence suggests that mupirocin may be as effective as chlortetracycline, fusidic acid, neomycin and other antibacterial agents, but more controlled, comparative studies are needed. The evidence of efficacy against nasal carriage of Staphylococcus aureus, including methicillin-resistant forms, is encouraging and currently work is being undertaken to improve the acceptability of the vehicle for this use. Side effects are limited to local reactions (in less than 3% of patients) and are no more frequent than observed with the vehicle alone. Thus, mupirocin appears to be a useful addition to the agents available for the treatment of superficial primary skin infections, such as impetigo, although its precise place in therapy remains to be established.