The study has as its objectives an understanding of the normal regulation of growth hormone and prolactin secretion from the pituitary; and attempts to gain some insight into the pathophysiologic mechanisms of disordered hormone secretion. A variety of animal and human experimental approaches are used. Pituitary culture systems, perifusion systems, isolated cell populations, pituitary tumor culture systems and in vivo experiments in both man and animals are employed. Hormone release is quantitated by radioimmunoassays. Many hormonal interactions are studied, including effects of prolactin on gonadotropins, effects of thyroid hormones on prolactin and growth hormone secretion, effects of sex steroids on prolactin secretion. The regulators of growth hormone secretion are studied, especially somatostatin production by the hypothalamus and its regulation; growth hormone releasing factors are prepared and studied for their effect on pituitary hormone secretion, cellular cyclic nucleotide levels and prostaglandin levels.