3-Methylfentanyl ("China White") is a "designer" opiate that has caused more than 100 overdose deaths in California since 1979, but that has not been associated previously with deaths east of the Rocky Mountains. During 1988, 3-methylfentanyl was identified in 16 fatal overdose cases in Allegheny County, Pennsylvania, contributing to a fourfold rise in overdose mortality during October of that year. Morphine was detected in the blood of five persons (31%) and cocaine in the blood of three persons (19%) dying of 3-methylfentanyl overdoses; these were demographically similar to 99 other fatal overdose cases investigated by the county coroner from 1986 through 1988. This documents the contribution of 3-methylfentanyl to overdose mortality in an eastern city and the use of 3-methylfentanyl with other illegal drugs. Drug abusers in the northeastern United States should be considered at risk for more "designer drug" overdose outbreaks in the future.