Roger Charles Louis Guillemin is a French-born American physiologist, who was awarded the ‘Nobel Prize for Medicine or Physiology’ in 1977, jointly with Polish-American endocrinologist Andrew V. Schally, and American medical physicist Rosalyn Sussman Yalow. Guillemin is distinguished as one of the pioneers in the field of neuroendocrinological research, the study of synergy of the central nervous system with that of the endocrine glands like the pancreas, thyroid and pituitary. He concentrated in examining the production of hormones by the brain and the effect of such hormones on the body. The hypothesis that hypothalamus, a portion of the brain, releases hormones that controls the pituitary gland, a theory which was first suggested by English anatomist Geoffrey W. Harris, was proved to be correct by Guillemin. His studies paved way for scientific pursuits and developments that helped in comprehending the physiology of brain and problems related to infertility, diabetes of juveniles and thyroid disorders. He examined the fibroblast growth factors receptors which are presently applied in diseases like diabetic blindness and for treating other eye related problems. His research work also included study of activins and inhibins, the peptides that aid in controlling the menstrual cycle. He is recipient of several awards and honours which include the ‘French Legion of Honor’ (1973), ‘National Academy of Sciences’ (1974), ‘Lasker Award’ (1975), ‘National Medal of Science’ (1976) and the ‘Dickson Prize in Medicine’ (1976).