The concentrations of arsenic, manganese and selenium/g wet tissue weight were determined in samples from 24 areas of the human brain from 3 patients with chronic renal insufficiency, 2 with Parkinson's disease and 1 with amyotrophic lateral sclerosis. The concentrations of the 3 elements were determined for each sample by neutron activation analysis with radiochemical separation. Overall arsenic concentrations were about 2.5 times higher in patients with chronic renal failure than in controls, and lower than normal in the patients with Parkinson's disease and amyotrophic lateral sclerosis. There were no obvious differences in the overall concentrations of manganese and selenium from one group to another. Even multivariate data analysis by the SIMCA method failed to reveal any significant difference in the distribution pattern of manganese and selenium in Parkinson's disease compared to normal controls.