In 1979 an indirect haemagglutination test (gonococcal antibody test) using gonococcal pilus antigen replaced the gonococcal complement fixation test as our routine procedure to show gonococcal antibodies. In the diagnosis of current gonorrhoea the sensitivity of the gonococcal antibody test was far superior to that of the gonococcal complement fixation test (about 55% versus 9% for first episode gonorrhoea). To evaluate the usefulness of the test result the following population groups were studied: 1376 patients undergoing medical examination for gonorrhoea (386 had gonorrhoea), 1384 healthy people aged 15-65, 54 patients with meningococcal disease, 30 children with respiratory tract infection, and 254 patients with evidence of various diseases other than neisserial infections that might be associated with symptoms of arthritis. These investigations showed that (1) non-specific positive gonococcal antibody test results occur rarely, (2) at least half the people who have had gonorrhoea remain seropositive (with titres of 1/40 to 1/160), and (3) a positive test result is more significant the younger the patient and the higher the titre. For younger people a positive test result should always be followed up by bacteriological examination; in all age groups titres of 1/320 or more should indicate medical examination for current gonorrhoea.