Vitamin D therapy for patients with end-stage renal disease (ESRD) on hemodialysis therapy has relied on patient dry weight to determine the initial dose of medication. Obtaining a patient's dry weight can be difficult, and no correlation has been established between a patient's body weight and severity of secondary hyperparathyroidism. We conducted a double-blind, double-dummy, randomized, 12-week, multicenter trial to compare the incidence of hypercalcemia (single occurrence) between two dosing regimens: one regimen based on baseline intact parathyroid hormone (iPTH; PTH/80) level, and the other regimen based on patient body weight (0.04 microgram/kg). One hundred twenty-five adult patients with ESRD on maintenance hemodialysis therapy were enrolled at multiple sites. Before treatment, all patients were required to have PTH levels of 300 pg/mL or greater, calcium levels of 8.0 mg/dL or greater and 10.5 mg/dL or less, and a calcium x phosphorus (Ca x P) product of 70 or less. Patients were randomized to one of two regimens: the nonrandomized treatment was also administered as a placebo dummy. No incidence of hypercalcemia occurred in either treatment group during the study. Patients treated according to the formula iPTH/80 required fewer dose adjustments and achieved the first of four consecutive reductions from baseline PTH level of 30% or greater more rapidly than patients treated based on body weight (P = 0.0306). Incidences of elevated Ca x P product levels were similar between treatment groups. Treatment with paricalcitol injection based on degree of secondary hyperparathyroidism incurred no greater risk for hypercalcemia and achieved meaningful therapeutic results with fewer dose adjustments than dosing based on patient body weight.