OBJECTIVE: To investigate trends in sexually transmitted diseases (STDs) among female commercial sex workers and in their condom use patterns during the period from 1990 to 1993 in Fukuoka, Japan. METHODS: The study group consisted of a total of 824 commercial sex workers who attended an STD clinic to undergo screening for STDs including chlamydia, gonorrhoea, syphilis, hepatitis B and HIV-1 infection during the period from 1990 to 1993. For detection of Chlamydia trachomatis and Neisseria gonorrhoeae, endocervical smear specimens were taken from the women. Blood samples were obtained for serological diagnosis of syphilis, hepatitis B and HIV-1. Commercial sex workers who visited the clinic during the period from November to December of 1993 were interviewed concerning past (1990 and 1991) and recent (1992 and 1993) condom use patterns. RESULTS: The annual detection rates of C trachomatis and N gonorrhoeae declined significantly from 16.3% in 1990 to 12.2% in 1993 (P < 0.0001) and from 1.5% in 1990 to 0.8% in 1993 (P = 0.0096), respectively. There was a remarkable reduction in the annual syphilis infection rate, from 7.5% in 1990 to 0.5% in 1993 (P = 0.0011). The positive rate for the hepatitis B surface antigen in the women ranged from only 0.6% to 1.9% and none were found to be positive for HIV-1 during the 4-year period. During the same period, there was a significant increase in the proportion of commercial sex workers always using condoms from 6.3% in 1990-91 to 25.3% in 1992-93 (P = 0.0023). CONCLUSION: The prevalences of chlamydia, gonorrhoea, and syphilis infections decreased significantly among commercial sex workers in Fukuoka from 1990 through 1993, and no commercial sex workers were HIV-1 seropositive. The reductions in the prevalence of major STDs may be related to the increased use of condoms.