Glucose tolerance was assessed in 100 cases of adrenocortical hyperfunction (79-Cushing's disease and 21-Cushing's syndrome). Overt diabetes was found in 19 cases. Of the remaining 81 patients 37 had normal glucose tolerance, in 23 glucose tolerance was impaired and in 21 patients diabetes was diagnosed. Glucose tolerance expressed as 60 and 120 min glucose values did no correlate with hormonal parameters of adrenocortical hyperfunction nor with age of the patients and degree of obesity. The authors discuss the complex mechanism of the effect of glucocorticoid excess on glucose tolerance.