IN EARLIER studies, we attempted to define the source of the organism causing staphylococcal endocarditis in drug abusers who used the needle. Street heroin and injection paraphernalia were not implicated.1We then found a 300% increase in the carrier rate ofStaphylococcus aureusamong those who had recently used drugs parenterally, compared to a control population who had not. Users who had not injected any drug for two weeks or more had the same carrier rate as the control group.2The reason for the increased carrier rate in recent drug users was not apparent, although we suspected that it might have been related to the effect of drugs on resistance to theStaphylococcusor on such epidemiologic factors as poor hygiene or frequent needle use. To examine the possibility that epidemiologic factors were involved, we have examined members of another group of patients who inject themselves regularly with