In a 5-yr randomized prospective study we examined the treatment effect of estrogen replacement therapy/hormone replacement therapy (ERT/HRT), calcitriol, ERT/HRT and calcitriol, or placebo for 3 yr and the effect of discontinuation of therapy for 2 more yr on bone mineral density (BMD), calciotropic hormones, markers of bone remodeling, and calcium absorption in 489 elderly women. The treatment phase of the study was double-blinded. After discontinuing therapy for 2 yr, there was rapid bone loss in all 3 treatment groups, and most of the decrease in BMD occurred in the first year. In the ERT/HRT group, spine BMD increased 5.5% in yr 3, decreased 3.2% in yr 4, and decreased 0.7% in yr 5; femoral neck BMD increased 3.7% in yr 3, decreased 2.5% in yr 4, and decreased 0.4% in yr 5; total body BMD increased 2.1% in yr 3, decreased 1.4% in yr 4, and decreased 0.6% in yr 5. In the combination group, spine BMD increased 7.1% in yr 3, decreased 4.3% in yr 4, and decreased 0.3% in yr 5; femoral neck BMD increased 4.5% in yr 3, decreased 3.0% in yr 4, and decreased 0.01% in yr 5; total body BMD increased 2.2% in yr 3, decreased 1.5% in yr 4, and decreased 0.6% in yr 5. In the calcitriol group, spine BMD increased 1.8% in yr 3, decreased 1.8% in yr 4, and showed no change in yr 5; femoral neck BMD increased 0.2% in yr 3, decreased 0.2% in yr 4, and decreased 0.6% in yr 5; total body BMD decreased 0.4% in yr 3, decreased 0.6% in yr 4, and decreased 0.4% in yr 5. Compared with placebo, all treated groups at yr 5 had significantly higher total body BMD; only the combination group had significantly higher spine BMD (3.4%; P < 0.001) and total hip BMD (2.4%; P < 0.01.) compared with the placebo group. Compared with baseline, only spine BMD in the combination group was significantly higher (2.6%; P < 0.001) at yr 5. The increase in calcium absorption and the decrease in serum PTH levels in the calcitriol groups were reversed after discontinuation of treatment, and the decrease in bone markers was reversed in the hormone-treated groups. These results suggest that discontinuation of ERT/HRT and/or calcitriol therapy in elderly women leads to a decrease in much of the BMD gained on treatment; however, in the combination group there was a statistically significant residual effect on spine BMD.