The biological aspects of depressive syndromes was the topic choosen for the fourth round table organized by the Esteve Foundation, held on February 4, 1987 and moderated by Jesús García Sevilla, from the Department of Pharmacology and Therapeutics of the Basque Country University. A total of eleven investigators submitted issues like diagnosis and classification of affective disorders, mechanisms of action of antidepressant drugs, or investigations like polygraphic studies of sleep or the TRH challenge test in depression. All are included in Dr. Antonio Esteve’s Monograph number 5.