We measured calcium regulating hormones and bone mineral density (BMD) in 66 men (aged 24-88 years). Vitamin D (1,25(OH)2D) does not vary with age, parathyroid hormone (PTH) increases after the age of 65 (p < 0.01) together with a parallel increase in urinary (r = 0.46, p < 0.05) and nephrogenic cAMP (r = 0.63, p < 0.01), while BMD decreases with age (r = -0.52, p < 0.01). The finding of age-associated decreases in bone mass even in the presence of constant serum levels of 1,25(OH)2D within the normal range suggests that there is an onset of tissue resistance to vitamin D in the aetiopathogenesis of osteopenia in elderly men.