Benzyl penicillin has been used extensively for ∼40 years in the treatment of gonorrhoea. The intense selective pressures resulting from the continual exposure of Neisseria gonorrhoeae to penicillin have resulted in the emergence of resistant strains that produce altered forms of penicillin-binding proteins (PBPs) with decreased affinity for the antibiotic^1–3. A comparison of the sequences of the PBP-2 genes from penicillin-sensitive and penicillin-resistant strains, suggests that penicillin-resistant forms of PBP 2 may have arisen both by amino-acid substitutions and insertions, and by the exchange of a region encoding part of the penicillin-sensitive transpeptidase domain with the homologous region from a closely related species.