The research sought to examine a new aspect of drug purity and the conditions under which addicts use drugs. Results revealed that 93.4 percent of the samples contained cadmium, always at high concentration; this metal resulted from addicts’ use of thinners and excipients containing salts of this metal to adulterate the heroin. In addition, all samples contained variable amounts of zinc and substantial amounts of iron, probably because it is the most common metal found in metal containers used n the extract of morphine from the opium poppy. Cadmium is the only metal studied that is regarded as toxic. Findings indicated that the potential toxicity of the metals studied at the concentrations found is relatively low. Only cadmium, and, to a lesser extent, zinc and copper and always at the highest concentrations found, might add to the intrinsic toxic effect of the drug. Tables and 17 references (Author abstract modified)