An enzyme immunoassay was used to determine IgM, IgG, and IgA antibodies to gonococcal pili in 68 patients with uncomplicated gonorrhoea, 35 women with pelvic inflammatory disease, and in 115 normal controls. A clear difference in response rate in all three antibody classes between patients with gonorrhoea and healthy controls was evident. Among women with gonorrhoea, the magnitude of antibody response was higher than among men with gonorrhoea, especially in the IgM class. No major differences were found in the overall distribution of serological findings between women with uncomplicated gonorrhoea and those with gonococcal pelvic inflammatory disease. Among this last group, however, high IgM antibody levels in acute phase sera were significantly associated with the isolation of Neisseria gonorrhoeae in the upper genital tract.