Low bone mineral density (BMD) is common in dialysis patients. Low BMD predicts the fracture risk in the general population. Bisphosphonate therapy improves BMD and lowers the fracture risk in many populations, but has not been tested in dialysis patients because of concerns about toxicity. In this investigation, the effect of a short course of alendronate on BMD in haemodialysis (HD) patients is evaluated. Thirty-one healthy HD patients were randomized to placebo versus 40 mg alendronate, taken once a week for 6 weeks. Hip and lumbar spine BMD were measured by dual energy X-ray absorptiometry at baseline and at 6 months. Osteocalcin, parathyroid hormone, calcium, phosphorous and alkaline phosphatase levels were assayed at baseline and at 1, 3 and 6 months. The BMD and T-scores in specific regions of the hip were stable in the treatment group and decreased in the placebo group (P=0.05). The lumbar spine density increased minimally in both groups. In the treatment group, osteocalcin levels declined significantly at 1 month (P<0.05) and remained low. The main side-effect in the alendronate group was occurrence of gastroesophageal reflux symptoms in three subjects. Low-dose alendronate, administered for a limited duration, appears to be well tolerated in dialysis patients. The BMD and T-scores declined at certain hip regions in the placebo group over 6 months, while remaining stable in the treatment group, suggesting a bone-preserving effect of alendronate. Further studies of longer duration, and including examination of bone histology, are needed to assess whether bisphosphonates can be used to preserve BMD in dialysis patients.