We have studied the effect on ototoxicity of maintaining serum calcium concentration by calcium gluconate infusion in cancer patients receiving high-dose cisplatin in a randomized study in two groups: 11 patients received calcium gluconate, 4 mg kg-1 i.v. infusion during cisplatin therapy; 11 other patients without any calcium supplementation served as controls. All of them received the first course of chemotherapy, based on cisplatin, 120 mg m2 with a hydration schedule. An audiogram was performed in each patient just before cisplatin and repeated after 1 day and 3 weeks. Mean total calcium concentration in control patients before and after chemotherapy was 2.2 +/- 0.14 (95% confidence interval 1.9-2.5) and 2.0 +/- 0.13 (95% CI 1.7-2.24) mmol 1(-1) respectively (P = 0.0004) and for ionized calcium 1.22 +/- 0.52 (95% CI 0.21-2.23) and 1.11 +/- 0.07 (95% CI 0.97-1.25) mmol 1(-1) respectively (P = 0.0005). Serum magnesium levels were maintained or increased by magnesium supplementation. Although there was no change in serum total or ionized calcium, or serum magnesium in the calcium infusion group, no differences in hearing loss between the groups were observed. High-dose cisplatin chemotherapy for cancer patients induces an acute decrease of serum total calcium and serum ionized calcium and audiometric changes. Maintenance of calcium serum levels by calcium gluconate infusion did not protect against ototoxicity in those patients.