Infection with new viruses and concomitant alcohol abuse cause increasingly severe hepatic and virological complications of parenteral drug abuse. The hepatitis delta virus (HDV), present only in conjunction with HBV, may cause progressive and clinically significant liver disease. Liver cirrhosis is frequently detected in parenteral drug abusers infected with both HBV and HDV viruses or who abuse alcohol. More than one-quarter of those in the U.S. with acquired immunodeficiency syndrome (AIDS) are homosexual or heterosexual men who are parenteral drug abusers. Parenteral drug abusers probably spread hepatitis viruses and the retrovirus associated with AIDS to the general population. Intensive international cooperation in data collection, research, and dialogue on effective measures to deal with parenteral drug abuse and its complications are recommended. 1 table and 33 references. (Author abstract modified)