A theoretical problem of interpreting the recently reported increase in homosexual gonorrhoea.

There has been considerable interest recently in using the occurrence of gonorrhoea infection as an indicator of sexual behaviour relevant to the transmission of human immunodeficiency virus. Mathematical models of gonorrhoea transmission can predict increasing incidence with decreasing sexual activity in the population, due to a resultant concentration of sexual activity in an active 'core' group. Increases in the incidence of gonorrhoea reported recently should therefore be interpreted with caution.