In order to explore the possibility of there occurring, in accordance with the Law of Mass Action, a reversal of the deposition of the cholesterol-lipoid-lipoprotein complex (Bevans et al., 1951), in the walls of cerebral arteries of atherosclerotic dements following a reduction in serum cholesterol, a study was made in March 1959 of changes that were shown in the behaviour of six such patients compared with six senile dements and four schizophrenics following the intake of large quantities of corn oil (Keys, 1956; Anderson et al., 1957).