We report a patient with squamous cell carcinoma of bronchus who developed the syndrome of inappropriate antidiuretic hormone secretion (SIADH) after receiving cisplatinum (CDDP) and vindesine (VDS). The 75-year-old man developed right chest pain and was found to have a squamous cell carcinoma of bronchus (stage IIIA, T3N1M0). He was treated by CDDP and VDS. The serum sodium concentration decreased from 136 mEq/l to 120 mEq/l after drug administration. SIADH was diagnosed on the basis of hyponatremia with corresponding serum hypoosmolality and an inappropriately high urinary osmolality due to continued sodium excretion. In our case, SI-ADH was probably induced by CDDP or VDS. Fluid restriction and sodium supplement resulted in a progressive rise in the serum sodium level to 134 mEq/l in 4 days.