Background: Calcium channel antagonist therapy in humans has been associated with changes in anterior pituitary, thyroid and adrenal hormone secretion. Human studies assessing effects of calcium channel antagonists on calciotropic hormones have been few and typically involved small numbers of subjects studied for short periods of time. Few of these previously published studies have included women. The endocrine effects of calcium channel antagonists in women have become increasingly important as more women are taking these agents for diseases such as hypertension, angina, Raynaud's phenomenon and migraine. Objective: To assess both acute and chronic effects of calcium channel antagonists on calciotropic hormones in women. Design: A four-week prospective, randomized trial. Subjects: Twenty-nine premenopausal women, randomly assigned to receive either 240 mg of sustained release verapamil or 30 mg of sustained release nifedipine daily. Laboratory end-points: Total and ionized serum calcium, phosphate, creatinine, parathyroid hormone (pTH), parathyroid hormone-related protein (pTHrP) and calcitonin, measured at baseline, after 24 hours, and 28 days of treatment. Results: Total and ionized calcium, phosphate, creatinine, pTHrP and calcitonin levels were not altered significantly after 24 hours or 28 days in any of the subjects, when compared to baseline. There were no significant differences in PTH levels after 24 hours or 28 days of verapamil treatment. There was a significant increase in serum PTH levels after 24 hours of nifedipine therapy; however, these differences were not evident after 28 days of therapy. Conclusions: The short-term administration of nifedipine results in increased release of parathyroid hormone; however, long-term administration has no significant effect on the concentrations of calciotropic hormones.