AIMS--The variable distribution of gonococcal serovars in different areas is well recognised but the factors that are important determinants of serovar prevalence are less clear. The aim of this study was to identify relevant clinical variables by comparing serovar prevalence in two cities over the same time period. METHODS--A prospective analysis of serovar prevalence was made between January and December 1992 in Edinburgh and Newcastle with respect to age, sex, sexual orientation, antibiotic sensitivity and presence of symptoms. RESULTS--224 infective episodes of gonorrhoea were studied. The serovar distribution varied between the two cities with serovar 1B-1 being more common in Edinburgh (20/91 cf. 4/133, p < 0.01) and serovar 1B-6 more common in Newcastle (26/133 cf. 2/91, p < 0.01). Serovar 1A-2 was associated with heterosexual infection (35/114 in heterosexuals cf. 0/85 in homosexuals, p < 0.01) and was more sensitive to penicillin than average (39/39 1A-2 strains highly penicillin sensitive cf. 98/184 for all other strains, p < 0.01) whilst 1B-6 was mostly acquired through homosexual contact (22/26 cf. 63/142 for all other strains, p < 0.01) and tended to show reduced penicillin susceptibility (13/28 1B-6 strains less penicillin sensitive cf. 45/195 for all other strains, p < 0.01). Infection with serovar 1A-2 was significantly less often symptomatic in heterosexuals than average (15/33 asymptomatic 1A-2 infections cf. 17/59 for all other serovars, p = 0.015). Subgroup analysis of male heterosexual infections confirms an association between asymptomatic infection and serovar 1A-2 (2/14 asymptomatic 1A-2 infections cf. 1/72 for all other serovars, p = 0.02). The distribution of infections over the year differed between the cities. CONCLUSIONS--A variety of factors including penicillin sensitivity and virulence may be important in determining the prevalence of gonococcal serovars within a given area.