All cases of gonorrhoea caused by penicillinase producing strains of Neisseria gonorrhoeae (PPNG) occurring in the population served by the West Midlands Regional Health Authority were surveyed. Isolates that were subjected to plasmid analysis were found to be mainly the "Asian" type in travellers from abroad and their immediate contacts, whereas isolates apparently indigenous in origin were mainly "African" type. The emerging sigmoid curve of yearly incidence, which is apparent for both the country and the region, may indicate that a dynamic equilibrium is being approached in the susceptible core populations. The importance of vigorous contact tracing is underlined by the contrast between the incidence of PPNG strains in the United Kingdom and the larger numbers found in areas where they are hyperendemic and where contact tracing is ineffectual or non-existent.