From May 1989 through November 1990, eight episodes of elemental mercury exposure in private residences or schools in the United States were reported to the Agency for Toxic Substances and Disease Registry (ATSDR). The case studies in this report document two of these episodes (both in Michigan) of residential mercury poisoning--one involving acute mercury exposure, and the other, chronic exposure to elemental mercury. These episodes illustrate the differing clinical and toxicologic manifestations of acute and chronic mercury poisoning.