Two patients developed dementia, erethism, colitis, and renal failure following the chronic ingestion of a laxative containing calomel (mercurous chloride). Brains of both patients were small and showed loss of cerebellar granular cells. Histochemical stains demonstrated mercury granules within the cytoplasm of neurons, particularly those of the inferior olive and dentate nucleus, and in the choroid plexus. Electron microscopy showed ultradense particles in the basement membrane of the choroid plexus; these were similar to but smaller than those in the kidney that electron diffraction analysis showed to be β-mercuric sulfide. Tissue mercury levels were elevated in both cases. In patient 1, the kidney level was 421μg/gm, and levels from 21 areas within the brain ranged from 105μg to 0.13μg/gm. Highest levels were in the inferior olive, red nucleus, and choroid plexus.