The somatostatin (SST) gene was analyzed to detect possible molecular variations in subjects with familial isolated growth hormone deficiency type I (IGHD I). No gross alterations in restriction fragments were observed with 18 used enzymes. The association with two RFLPs closely linked to the SST gene was also negative, adding weight to the evidence that the SST gene is not involved in the etiology of IGHD I. The nucleotide variability of a 23-kb DNA segment containing the SST gene and its flanking sequences was studied by restriction analysis of a sample of 19 Italians. The data suggest that approximately 1 in 400 bp is variant in this region.