The population of Curaçao, Netherlands Antilles (133,000) shows a very high prevalence of end-stage renal disease (approximately 1 per 1,000). These patients are often treated chronically with haemodialysis. As the drinking water on the island is prepared by distillation of sea water, the haemodialysis fluid used to be prepared with tap water without further treatment. In 1996, the 27 patients of one of the dialysis centers on the island presented with nausea, vomiting, and hypercalcaemia in a short time span, which was initially diagnosed as 'hard water syndrome'. In spite of treatment with low-calcium dialysate, microcytic anaemia and neurological symptoms developed. Ten patients died of convulsions, sepsis, and coma. As aluminum (Al) intoxication was suspected, Al in serum (AlS) was measured. Ante mortem AlS was 808 microg/l (n = 7; range 359-1189); in the survivors AlS was 255 microg/l (n = 17; range 113-490). Normal AlS is < 10 microg/l, and <50 microg/l in asymptomatic dialyzed patients. The court requested post-mortem toxicological analysis of four patients. Al concentrations in liver, bone, and cerebral cortex were significantly increased as compared with background levels. Al intoxication was, therefore, considered to be the most likely cause of death in these patients. Investigations of the tap water supply revealed that a few weeks before the onset of the symptoms, a water conduit pipe to the dialysis unit had been replaced, which was lined with Al- and Ca-rich cement mortar. These ions leached into the distilled water and caused both Ca- and Al-intoxication through uptake from the dialysate into the patients' circulation. The symptoms of the latter were initially not recognized as they were masked by the symptoms of hypercalcaemia.