Deficiency of protein Gs (Gs; OMIM no.103580), the stimulatory regulator of adenylyl cyclase, is associated with resistance to PTH and other hormones, sc calcifications, short stature, and skeletal defects (Albright's hereditary osteodystrophy). It is caused by heterozygous loss of function mutations in GNAS 1, the gene encoding the alpha-subunit of Gs. Obesity is a classical feature of patients with Gs deficiency, but the mechanism leading to fat accumulation has not been elucidated. We measured glycerol flux, using a nonradioactive tracer dilution approach, to analyze the lipolytic response to epinephrine in 6 patients with Gs deficiency and PTH resistance and compared it to six age-matched normal controls and nine massively obese children. Basal glycerol production was reduced by 50%, and lipolytic response to epinephrine was reduced by 67%, in Gs-deficient children, as compared with controls. The degree of impairment of lipolysis was similar in Gs-deficient children who were only moderately overweight and in morbidly obese children. These findings extend the spectrum of hormonal resistance in Gs deficiency. Besides beta-adrenergic receptors, Gs protein itself should be examined as a possible step involved in the decreased lipolysis observed in common obesity.