The 24 hr variations of plasma growth hormone (GH) and/or GH secretion provoked by oral glucose load or by insulin-induced hypoglycemia were studied in five microcephalic children. Low levels of GH and, especially, complete lack of secretory episodes were detected in three of the five children, two of whom were brothers. GH deficiency may constitute the principal or a contributing factor of impaired growth in some microcephalic children. A possible association between the cerebral abnomality and the pituitary hypofunction is suggested. An analogy is made between the present cases and the neuroendocrine complexes reported as Kallmann's and de Morsier's syndromes, respectively.