This is a synthetic presentation of the data accumulated along almost fourty years in the Institute of Endocrinology in Bucharest, on the biology of the pineal gland. Most of these were included in the book treating on the pineal gland as an organ of metabolic regulation. The works revealed hypoglycemic, anabolic, anticholesterolemic and glomerulotrophic action of the pineal peptides as opposed to the pinealectomy which induced completely opposite effects. It was also demonstrated that the pineal gland has an antisteroid action, being both anticorticosteroid and antiandrogenic; the antigonadotropic action was also revealed on the basis of the classical method in endocrinology in which two states of plus or of minus of the glandular secretions show diametrically opposed phenomena. Researches on the hormonology of the pineal gland led to the production of a biologically active peptide extract which was finally turned into a medicine under the name of Crinofizin. The therapeutic indications of this drug are also presented.