Isolated growth hormone (GH) deficiency (IGHD) is detected in 1/10 of pituitary dwarfism, but there are only a few reports on IGHD as an autosomal-dominant trait. We found one family with autosomal-dominantly inherited IGHD and examined their pituitary functions and GH genomes. Brothers (9.5 year and 11 year) and their mother (37 year) were diagnosed as having IGHD and their grandmother and uncle also seemed to have IGHD. All of their heights were under "mean-4.0 S.D.". Cerebral tomography of brothers and their mother all showed "empty sella", and GH-releasing hormone (GRH) tests showed no responses of GH not only to bolus intravenous injections but also after repeated intramuscular injections of GRH (100 micrograms/day) for 7 days. Although genetic analysis (Southern blotting method) could not detect any mutations in their GH genomes, the IGHD lesion of them seemed to be pituitary in origin.