Patients with primary hyperparathyroidism (pHPT) are sometimes treated with bisphosphonates (BPs) as an alternative to surgery despite sparse documentation of the efficacy in this disorder. It is therefore of interest to study the biochemical effects from BPs in patients with pHPT. A series of 21 pHPT patients with serum calcium levels > 2.8 mmol/L were included. One month before surgery the patients underwent intravenous infusions of 30 to 40 mg pamidronate. Study parameters were total and ionized serum calcium, intact parathormone (PTH), alkaline phosphatase (ALP) and isoenzymes, creatinine, osteocalcin, 25-OH vitamin D(3), 1,25-OH(2 )vitamin D(3), urine calcium/creatinine, and osmolality. Registration of hypercalcemia-related symptoms were done by questionnaire. After pamidronate there was a temporary reduction in serum calcium with a nadir at 6 to 10 days. Normalization of serum calcium was achieved only by surgery. Intact PTH rose after pamidronate, with a maximum on day 6. Urinary calcium excretion was reduced after both pamidronate and surgery. ALP was reduced 30 days after pamidronate and also after surgery. Serum osteocalcin was not influenced by pamidronate. No statistically significant differences in symptoms were reported after treatment. In conclusion, there was a short, limited calcium-lowering effect from pamidronate in pHPT patients and a transient increase in PTH corresponding to the reduced calcium concentration. An obvious change in bone markers was found only after surgery. Treatment with BPs should not be considered an alternative to surgery, which is still the only method to cure patients with pHPT.