The authors studied the annual incidence of isolation of penicillinase-producing Neisseria gonorrhoeae (PPNG) strains among the total number of strains of N. gonorrhoeae (1,401 strains) that were isolated in Sapporo, Japan during 1980-1989. During the first half of the 1980s, there was a tendency for PPNG to increase, and the peak incidence was 23.9% in 1985. Thereafter, the incidence of PPNG decreased to an isolation rate of 6.3% in 1989. In addition, the auxotypes of 592 of 1,401 isolated strains of Neisseria gonorrhoeae were studied during three periods: 1980-1985, 1986-1987, and 1988-1989. Among the 592 strains, 315 strains were tested for sensitivity to the action of amoxicillin. In the 1988-1989 period, the auxotype showed an increasing incidence of the auxotype that requires arginine, hypoxanthine, and uracil (i.e., AHU), whereas the proto- and pro-types decreased in incidence. The AHU strains showed higher sensitivity to amoxicillin administration compared with the proto- and pro-strains.