The emergence of penicillinase-producing Neisseria gonorrhoeae (PPNG) strains in 1976 and the increasing frequency of chromosomally mediated resistance to penicillin has resulted in a decline in the effectiveness of penicillin for the treatment of gonorrhea. In Hong Kong, the emergence of bacterial resistance to kanamycin or tetracycline has also been observed. Quinolones were first introduced in Hong Kong in 1985, and since then the percentage of PPNG-related cases of gonorrhea has dropped dramatically. The use of quinolones for the treatment of nongonococcal urethritis has not been as successful as that for gonorrhea. Haemophilus ducreyi (the causative organism of chancroid) is sensitive to quinolones, and the occurrence of chancroid since 1985 has decreased from 628 to (in 1987) 184.