A non-clinic cohort of 525 homosexually active men from London and South Wales were recruited in 1988 for a study by interview of sexual behaviour. A sample of blood was tested for HIV-1 antibodies. Seropositivity in London was 9.2% compared with 3.4% in South Wales. Men who were not regular STD clinic attenders had a lower rate of seropositivity than did those who were regular attenders. Men who were seropositive reported more sexual partners with whom they had anal intercourse and also reported more episodes of syphilis. Overall, rates of seropositivity were lower than those reported by studies from STD clinics. AJ Hunt, G Christofinis, APM Coxon, PM Davies, TJ McManus, S Sutherland, P Weatherburn