The aim of the present study was to characterize endemic versus non-endemic gonorrhoea to identify risk groups for transmission and to evaluate the effects of intensified contact tracing performed by specially trained social workers at venereal clinics. A total of 671 gonorrhoea patients (283 women and 388 men) comprised the study group. Seventy percent of the women and 48% of the men had an endemic infection (P < 0.001). Men without a steady partner had an increased risk of non-endemic infection. A decrease from 75% to 40% was noted in the proportion of endemic infection in Stockholm from the first quarter of the study period (2 years) to the last. Contact tracing resulted in 1.2 identified partners per patient. A total of 736 partners were examined either as a result of contact tracing efforts or because they had sought medical care on their own prior to intervention. Forty-seven percent of these partners were infected, 44% were not infected and 9% were examined outside the study with results unknown to us. The partner notification efforts yielded 161 new untreated cases. Contact tracing of women generated one new case per 4.0 interviewed women and contact tracing of men one new case per 4.3 interviewed men. Interviewing index patients with endemic infection yielded the highest number of new cases. Forty-three percent of the patients were infected outside Stockholm but only a smaller part of these patients spread their infection further into the community.(ABSTRACT TRUNCATED AT 250 WORDS)