The IGF-I gene from leukocyte DNA of a control population of normal stature was studied using Southern blotting. Restriction fragment lengths for 21 enzymes were determined and three restriction fragment length polymorphisms (RFLP) were found (EcoRV, HindIII, and PvuII). In addition, the IGF-I gene of 64 constitutionally short subjects, five Pygmies, and 10 constitutionally tall subjects was analyzed. No IGF-I gene alterations were detectable by Southern blot in any of these conditions. Linkage analysis using genetic markers (RFLP) yielded results that were uninformative for five constitutionally short families investigated, owing to the limited number of RFLP and their low incidence (17% for the 5.2- kb HindIII, 5-kb PvuII RFLP alleles, and 13% for the 13- kb EcoRV RFLP allele). The EcoRV RFLP was found to map near Exon 1. The incidence of the 13-kb polymorphic allele with EcoRV proved to be lower (4%) in the group with constitutionally short stature than in controls. These results could suggest that modifications in the region of the IGF-I gene may be involved in constitutionally short subjects.