We studied an Argentinian family of Spanish ancestry in which the parents are of normal height and three of their four children have isolated GH deficiency type I-A. Restriction endonuclease analysis of DNA isolated from leukocytes was done using 32P-labeled human GH (hGH) cDNA sequences as a probe. The three siblings were homozygous, while their parents and the remaining sibling were heterozygous for a deletion of about 7.5 kilobases DNA, which included the normal hGH gene. The phenotype of the affected subjects differed in several respects. There was variation between the homozygotes in birth length and height before hGH treatment and growth responses during long term hGH treatment. Furthermore, heterozygotes in this family had normal height despite their diminished hGH responses to provocative tests.