Resistance of Neisseria gonorrhoeae to antimicrobial agents is increasing in the United States. The number of cases of gonorrhea caused by beta-lactamase-producing strains of N. gonorrhoeae (PPNG) increased for the second consecutive year, and 16,608 were reported in 1986; these accounted for greater than 1.6% of all cases of gonorrhea. PPNG is endemic in Florida, New York City, and Los Angeles, and these areas may serve as foci for spread of PPNG strains in the United States. In 1985 N. gonorrhoeae strains that exhibited high-level resistance to tetracycline (TRNG; MIC, greater than or equal to 16.0 micrograms/ml) were reported. Tetracycline resistance was due to the tetM determinant in a 25.2-MDa tetM-conjugative plasmid. The prevalence of TRNG infections was greater than 4% in at least two communities. Strains with chromosomally-mediated resistance to several antimicrobial agents have been isolated more often; 399 cases were reported during the first half of 1986. Spectinomycin-resistant strains have been isolated in several cities, and strains with decreased susceptibility to ceftriaxone have been isolated. Phenotypic characterizations of strains of N. gonorrhoeae by auxotype and serovar, plasmid content, and antibiograms have permitted more detailed study of the heterogeneity and dynamics of strain populations. Characterization of outbreaks caused by resistant strains and surveillance of regional and temporal changes in antimicrobial resistance in gonococcal strain populations may be used in design of innovative strategies for gonorrhea control and for making anticipatory changes in recommended therapies for gonorrhea.