Iatrogenic contamination of multidose vials in simulated use. A reassessment of current patient injection technique. An investigation of the potential spread of iatrogenic infections through contaminated multidose vials was performed. Contamination of a multidose vial was hypothesized to occur after a single syringe is used to inject an infected patient with medication, and the same syringe subsequently is used to withdraw additional medication from the multidose vial. If the contaminated multidose vial is used for another patient, an iatrogenic infection may be spread. Laboratory study of this injection technique found that viral plaque-forming units could be transmitted to a multidose vial in this manner. A survey of 100 fellows of the American Academy of Dermatology from the United States found that 24% of the respondents used this potentially unsafe procedure. The potential for iatrogenic spread of the human immunodeficiency virus and hepatitis B virus is described. Recommendations to avoid patient infection are made. 