Prostitutes are a major reservoir of sexually transmitted diseases in many developing nations. In Nairobi we found that 16%, 28%, and 46%, respectively, of upper-, middle-, and lower-social strata prostitutes were infected with Neisseria gonorrhoeae. Genital ulcers and infections with Haemophilus ducreyi were more prevalent among prostitutes of the middle and lower social strata. A group of 97 prostitutes of the lower social strata were followed longitudinally to determine the rate of reinfection with N. gonorrhoeae. The mean time to acquisition of a new infection was 12.0 +/- 9.2 days. These results show that in Nairobi prostitutes are a readily identifiable group of high-frequency transmitters of gonococcal infection. Strategies based on intervention in the prostitute reservoir could prove to be an effective means of control of gonococcal infections in developing nations.