Cherubin, C. E. (Harlem Hospital Medical Center, 136th St. and Lenox Ave., N.Y., N.Y. 10037), R. L Hargrove and A. M. Prince. The serum hepatitis related antigen (SH) in illicit drug users. Amer. J. Epid., 1970, 91: 510–517.—Sera taken from patients with hepatitis who denied drug usage, and from users of intravenous heroin and methamphetamine, with and without clinical evidence of hepatitis, were tested for the presence of the serum hepatitis related antigen (SH) by an Ouchterlony technique. Fifty-four % of in-patients with acute viral hepatitis who were known drug users had SH antigen in acute serum specimens. Two to three % of drug users without evidence of acute hepatitis also had detectable quantities of this antigen: By comparison, the frequency of antigen detection in volunteer blood donors was 0.1%. There was a correlation, in both acute hepatitis cases and in asymptomatic drug users, between the degree of serum glutamic pyruvic transaminase elevation and the presence of detectable SH antigen. Fifty % of sera from adolescents and young adults with hepatitis, at Harlem Hospital and New York Hospital, who denied drug usage were also positive for SH antigen. This suggests either that the addiction problem is far greater than previously surmised, or that other modes of transmission of SH antigen positive hepatitis exist in New York City. In any case it appears that the majority of adult cases of hepatitis occurring in this study were caused by this agent which may be specific for serum hepatitis.