Summary It is hypothesized that mental impairment decreases in patients with atherosclerosis treated with Premarin. One hundred and one patients were studied, 51 who had had cerebral thrombosis and 50 who had recovered from an acute myocardial infarction. The Rorschach test was first administered when the patients began either Premarin or placebo therapy, and was repeated after 6 to 16 months of treatment. The tests were assessed for indications of impairment in thinking, and each patient received a score denoting amount of increase or decrease in impairment after treatment. There was considerable overlap in scores between Premarin and placebo patients, and gains were relatively small for individual patients. Nevertheless, improved mental functioning was found in both cerebral and cardiac patients treated with Premarin in comparison with those on placebo, and a positive association was observed between Premarin therapy and decreased mental impairment.