Consecutively isolated gonococcal strains from 10 representative geographical areas in Sweden were serogrouped according to the previously described W antigen class. The majority of the strains were antibiotic susceptibility tested and approximately one fourth of them were auxotyped. Statistically significant differences of the serogroup patterns were demonstrated between the 2 largest towns, which represented highly urbanized areas where serogroup W II dominated, and the middle sized towns with adjoining rural districts, where serogroup W I dominated. The serogroup patterns of the strains isolated in 3 university towns were representative for Sweden as a whole. Statistically significant differences were demonstrated between urban and rural areas with regard to the susceptibility of gonococci to beta-lactam antibiotics. About 95% of serogroup W I strains were highly sensitive to ampicillin whereas about 65% and 90% of W II and W III strains, respectively, showed decreased susceptibility. The majority of the auxotyped strains belonged to 4 main types: Pro-, Pro-Arg-Ura-, AHU- and prototrophic. The majority of the AHU- strains belonged to serogroup W I and were highly susceptible to beta-lactam antibiotics and tetracycline. Many of the Pro-Arg-Ura-strains belonged to 2 particular subserogroups within serogroup W II and showed increased resistance to beta-lactam antibiotics. Serological classification of gonococci by co-agglutination is a simple and rapid technique without need of special equipment. It could serve 2 purposes: 1) as a confirmation test for gonococci cultured from clinical specimens; 2) for serogrouping of gonococcal isolates to study the epidemiology of gonorrhoea with regard to geographical areas, race, sexual preference, treatment failure and other demographic and medical factors.