With the aid of insulin-tolerance and arginine tolerance tests (ITT and ATT, respectively) somatotropic function of the hypophysis was assessed in 18 patients with hypophyseal nanism and in 12--with gonad dysgenesis. A marked delay in development and a premature exhaustion of the STH secretion was noted in the patients wiht hypophyseal nanism. In patients with gonad dysgenesis the STH secretion was somewhat redeced during the ITT. A change in the STH secretion was accompanied by a parallel depression of insulin secretion during the ATT. Patients with hypophyseal nanism displayed a correlation between the extent of growth delay and the value of the STH secretion during the ITT (R=0.6, P smaller than 0.05).