The case of a 41-year-old woman with cerebral calcification of a rather unusual extent is reported. This condition was associated with mental deficiency, pseudohypoparathyroidism and Albright's hereditary osteodystrophy. Four years later hypothyroidism was diagnosed. Visual impairment and electroretinogram abnormality suggested a retinopathy involving mostly rods. Despite their rarity, pseudohypoparathyroidism and Albright's hereditary osteodystrophy are of major interest, since they represent the only human disease states in which G protein function has been found to be disrupted. The overall clinical picture was strongly suggestive of a genetic deficiency of a guanine nucleotide-binding protein, termed Gs. The putative involvement of another G protein, contained in rods and cones, transducin, in the pathogenesis of the retinopathy is discussed.