We have conducted a randomized crossover comparative trial of a single-dose course of disodium (3-amino-1-hydroxypropylidene) bisphosphonate pentahydrate (pamidronate) and plicamycin in 48 patients with a first occurrence of tumor-related hypercalcemia. All patients had hypercalcaemia-associated symptoms and serum-calcium levels (corrected for total protein) greater than or equal to 2.80 mmol/l. Pamidronate and plicamycin were given concurrently with rehydration immediately after diagnosis of hypercalcaemia was made. Both agents lowered serum calcium levels significantly within 1 week, with 88% of the evaluable patients in the pamidronate group and 45% of those in the plicamycin group achieving normocalcemia (p less than 0.01). In the patients who received pamidronate, the duration of normocalcemia was longer (p less than 0.05) and there was a significant decrease in serum creatinine (p less than 0.05). Vomiting occurred in 8 of 22 evaluable patients (36%) who received plicamycin, but in none of 25 evaluable patients who received pamidronate (P less than 0.01). Phlebitis occurred at the infusion site in more of the pamidronate-treated patients (P less than 0.05). Hypocalcemia, which occurred in 8 of 25 evaluable patients (32%) in the pamidronate group and in 1 of 22 of those (5%) in the plicamycin group, was either clinically asymptomatic or mild, except in one pamidronate-treated patient. Overall, pamidronate was found to be more effective and better tolerated than plicamycin, thereby confirming results of previous studies that showed pamidronate to be an effective, simple, and safe agent for the relief of the morbidity associated with tumor-related hypercalcemia.