The effect of selenium (Se) in reducing the toxicity of cisplatin in cancer patients was studied. Forty-one patients were randomized into group A (20 patients with Se administration in first cycle of chemotherapy as study cases and without Se in second cycle of chemotherapy as control) and group B (21 patients without Se in first cycle of chemotherapy and with Se in second cycle of chemotherapy). The 4000 micrograms per day of Se as Seleno-Kappacarrageenan were administered from 4 before to 4 d after chemotherapy for study cases. The serum Se increased from 70.4 +/- 22.86 to 157.04 +/- 60.23 ng/mL (P < 0.001) in patients received Se. The cisplatin dosage was iv administration in 60-80 mg/m2 on the first day. The results showed that the peripheral WBC counts on day 14 after initiation of chemotherapy in study cases was significantly higher than the controls (3.35 +/- 2.01 vs 2.31 +/- 1.38 [x10(9)L])/L, p < 0.05). On the other hand, the consumption of GCSF for the cases was significantly less than the controls (110.1 +/- 82.2 vs 723.6 +/- 192.6 IU, p < 0.05). The volumes of blood transfusion for the study group were also significantly less than the controls (0 vs 62 +/- 38 mL, p < 0.05). The nephrotoxicity of cisplatin was measured by urine enzymes (NAG, GGT, AAP, LAP, and ALP) were determined prior to and at 2, 24, 48, and 72 h after initiation of chemotherapy. The urine enzymes NAG, GGT, AAP, and ALP after chemotherapy for cases were significantly lower than the controls. No toxicity of Seleno-Kappacarrageenan was noted. The above results suggest that the Se can be used as an agent for reducing the nephrotoxicity and bone marrow suppression induced by cisplatin.