In Colorado Springs, Colorado, between January and June 1981, approximately 400 cases of gonorrhea in heterosexual men generated approximately 200 "spread" cases in women. The ratio of spread cases to index cases (0.5) is an empiric measure of the reproductive rate for the disease, i.e., the rate at which an infected person replaces himself. Although a reproductive rate of less than one theoretically should produce extinction of the disease, the rate derived from these data is shown to be a weighted average of the rates in symptomatic men (0.31), subsymptomatic men (0.79), and asymptomatic men (1.30). Approximately 35% of gonorrhea transmitted by men may be attributed to the asymptomatic group, which constitutes 10-15% of the infected population. If the observations in this community are applied to the nation as a whole, we estimate that approximately 1.7 million cases of gonorrhea occurred in 1981, as compared with the 990,864 cases actually occurred in 1981, as compared with the 990,864 cases actually reported. This estimate is close to those usually quoted but differs in gender composition. Whereas the observed male-to-female ratio is 1.48:1, the predicted ratio, based on estimates of reproductive rates in subgroups, is 0.8. This analysis supports the theoretical notion that the endemicity of gonorrhea is maintained by heightened transmission within small groups, and it suggests that underdetection is more important than underreporting in the assessment of the "true" incidence of this infection.