An epidemiologic investigation of viral hepatitis among "street-people" was conducted in Pittsburgh, PA in 1971. Among 146 individuals, 100 admitted to parenteral drug use and 73 (50%) had evidence of acute viral hepatitis. Counterelectrophoresis (CEP) and complement-fixation (CF) were used to test for type B antigen (HBS AG). Seventeen individuals (22%) had detectable HBSAG; 13 of these were clinically ill and admitted to drug use, Type B antibody (anti-HBS) was tested for by CEP and radioimmunoprecipitation (RIP). Thirty-five persons (29%), 15 of whom admitted to drug use and were ill, had detectable antibody by RIP; none had detectable antibody by CEP. None of those tested had both HBSAB and anti-HBS Evidence to support the hypothesis of sexual transmission of type B virus was found. Use of prophylactic gamma globulin in street-people populations is recommended.