The effect of alendronate on calcium metabolism, PTH, bone mineral density and markers of bone turnover in 40 patients with primary hyperparathyroidism was investigated. The treatment group (n=40; T score −2.5 SD at the femoral neck or total radius) was treated by alendronate in 70 mg/wk for 12 months. The second group (n=20) was not treated due to different reasons. Patient examination was repeated in 6 and 12 months. The aim of the study was to compare the calcium, BMD and bone turnover markers dynamics in patients with nature progression of the disease and bisphosphonates treatment. Main results: We found that bisphosphonates treatment significantly reduced hypercalciemia and hypercalciuria, especially in the first 6 months and in most cases this effect retained up to 12 months. The BMD dynamics didn't differ between the groups, but every group included the patients having a good increase of BMD, and the patients in which the lowering of BMD still progressed. BMD increase in the alendronate group was noted in L2–L4 section in 18 (51%) patients who had received alendronate, in total hip — 18 (51%), and in total radius — 19 (59%). In the control group — in L2–L4 in 9 patients (53%), in total hip — 6 (35%), and in total radius — 7 (50%). The mean values (±sd) of the total calcium in the alendronate group was 2.69±0.19 mmol/l before treatment, and 2.6±0.16 mmol/l after 12 months, in the control group 2.62±0.24 mmol/l and 2.62± 0.13 mmol/l. 24 h calcium excretion in the alendronate group was 7.4±4.2 mmol/day before treatment, and 6.3±3.7 mmol/l after 12 months, in the control group 7.9±3.9 mmol/l and 6.8±3.2 mmol/l. Alendronate treatment was associated with perceptible reductions in bone turnover markers. In the alendronate group the OK distribution median and quartiles were 41.1 [27.8;61.8] before and 29.6 [20.7;34.6] 12 months after treatment, CTx values were 0.75 [0.50;1.20] before and 0.35 [0.30;0.53] 12 months after treatment. In the control group the same parameters were 34.1 [25.4;49.0], 31.2 [23.2;37.0], 0.70 [0.60;0.90], 0.70 [0.50;1.00]. The adverse effects of alendronate were rare. Two patients had complaints about swelling and diarrhea and changed alendronate to ibandronate. And two patients discontinued treatment because their state of health became worse and they were operated on. Conclusion: Alendronate treatment was associated with some benefits in indirect parameters of bone metabolism. Conflict of interest: None declared.