Prostitution in Sheffield, a city with over half a million population, has been reviewed in its legal, social work, and medical aspects. The years studied were 1960-73. The medical studies were confined to the years 1968-72. Prosecutions for soliciting increased steadily during the study period. The trend was more marked locally than nationally and was associated both with increased police activity and, more recently, with the pursuit of a socially-aware sentencing, probationary, and social work policy. During the 5-year medical study, sixty prostitutes were seen. Using gonorrhoea as an index they were found to hazard the health of both themselves and others. Recurrent infection was the rule amongst them and 40 per cent. suffered salpingitis. In epidemiological terms our findings show that the vector role of prostitutes continues undiminished. The alleged decline in their role is relative only and not real. They accounted for one in six of locally acquired gonococcal infections in heterosexual men. The study indicates the need for the regular monitoring of the social phenomenon or prostitution and for the detailed study of all its aspects on a national basis.