The pathophysiology of heroin "overdose" deaths is not fully understood. Surveillance of these deaths and of the heroin content of glassine bags available at the "street level" in Atlanta in the 1971-to-1973 period disclosed a significant correlation between the occurrence of such deaths and the amount of heroin contained in the bags (P<.001). Case histories of one cluster of deaths suggest that novice users with a low level of opiate tolerance could have died from intake of amounts of heroin in excess of their tolerance. However, the data are also consistent with causes other than pharmacologic overdose. (JAMA229:677-678, 1974)