An important concern in treatment for gonorrhea is the high frequency of coexisting chlarnydial and gonococcal infections. But there is difficulty in the diagnosing chlamydial infection. And so, CDC recommends epidemiological treatment, of both gonorrhea and non-gonococcal urethritis in the gonorrheal treatment in order to prevent post-gonococcal urethritis(PGU), A total of 140 male patients with uncomplicated gonococcal urethritis at the VD clinic, Choong-ku Publir. Health Center, in Seoul during December, 1987 February, 1988 were subjected to this study. The patients treated with kanamycin(KM), 2g and aqueous penicillin G(ACPG) 8 million units imaccompanied by probenecid(BEN) 1g by mouth. This combination regimen showed good effect in the treatment of gonococcal urethritis (failure rate 4.2% ). After gonorrheal treatment, the patients were divided randomly into group A and group B. In the group A, adminstrated with doxycycline monohydrate, 100mg, by mouth two times daily for 7 days, 44 and 29 patients were followed at 7th and 14th day after gonorrheal treatment. In the group B, administrated with placebo, 1 tablet, by mouth two times daily for 7 days, 49 and 39 patients were followed at 7th and 14th day after gonorrheal treatment. The PGU incidences were 27.3%(12/44), 20.7%(6,'29) in the group A and 55. 1%(27,'49), 53.8(21/39) in the group B at 7th and 14th day after gonorrheal treatment. Conclusively, eoncornitant administration of doxycycline monohydrate, 100mg, by mouth two times daily for 7 days with gonorrheal treatment lowered PGU significantly. (Kor J Dermatol 28(l): 34 38, 1990)