The distribution of serotypes of Chlamydia trachomatis in urogenital infection in Sapporo was studied by typing 30 isolates with Monoclonal antibodies and by testing patient sera from 134 individuals with the micro-immunofluorescence test. 1. Among 30 isolates, the majority of strains were identified to be types D and E (23%), followed by G (13%), F (10%), H (10%), I (7%) J (7%) and K (7%) in this order. 2. In 134 patients sera, the most frequent antibody types were B/ED (64.8%), followed by C/J (13.3%), G/F (7.8%), H/I/J (7.1%) and K (2.3%). Thus, serovar D and E were the same predominant type of Chlamydia trachomatis in urogenital infection in Sapporo, as in the USA and Europe.