Administration of ACTH results in an increased capacity for incorporation of C14-glycine into protein in cell-free preparations of rat adrenals containing microsomes, soluble cell fraction, and an exogenous ATP source. This stimulatory action of ACTH has been found to be due primarily to effects occurring in the soluble cell fraction. The effect of ACTH on adrenal protein synthesis in the rat has been further localized within the soluble cell fraction. Following ACTH administration, changes occur in the soluble cell fraction whereby the transfer of amino acid from amino acyl -S-RNA to protein is enhanced. This enhancement does not appear to be due to increased availability of ATP or GTP.