There is ample evidence that zinc plays an important role in bone metabolism and zinc deficiency has been implicated as a risk factor in the development of osteoporosis. It was the aim of the present study to investigate the skeletal effects of alimentary zinc deficiency in growing rats using quantitative bone histomorphometry. Twenty-four male Sprague Dawley rats with a mean initial body weight of 101 +/- 2 g were allocated in two groups of 12 rats each and had free access to a semi-synthetic, casein-based, zinc-deficient diet (0.76 mg zinc/kg) or to the same diet supplemented with 60 mg zinc per kg. All rats were sacrificed 42 days after the start of the experiment and the right distal femur was removed for bone histomorphometry. Relative to controls (+Zn), the zinc-deficient rats (-Zn) had a significantly lower body weight and about an 80% reduction in plasma and femur zinc concentration. The histomorphometric evaluation of the distal femoral metaphysis showed that zinc deficiency led to a 45% reduction (p < 0.01) in cancellous bone mass and to a deterioration of trabecular bone architecture, with fewer and thinner trabeculae. The osteopenia in -Zn rats was accompanied by significant reductions in osteoid perimeter (-31%, p < 0.05), osteoblast perimeter (-30%, p < 0.05), and osteoclast number (-38%, p < 0.01) relative to +Zn controls. We conclude that zinc deficiency induced low turnover osteopenia in femoral cancellous bone of growing rats. These results support the hypothesis that zinc deficiency during growth may impair the accumulation of maximal bone mass in humans; additionally, they suggest that zinc deficiency may play a role as a risk factor in the pathogenesis of osteoporosis.