In the present paper we employed adsorptive transfer stripping technique coupled with chronopotentiometric stripping analysis for determination of metallothionein (MT) in tumor cell lines and differential pulse voltammetry Brdicka reaction for determination of MT in blood serum of patients with head and neck cancer or retinoblastoma, and of rats treated with cisplatin with respect to discuss the role of MT in formation of resistance on treatment with heavy metal based cytostatics. The cisplatin or carboplatin sensitive and resistant neuroblastoma cell lines were derived from the maternal cell line isolated from the bone metastasis of patients with neuroblastoma. Based on the results obtained it can be concluded that level of MT increases with higher dose of platinum based cytostatics at cells. Further we focused on determination of MT in blood serum of rats treated with cisplatin (two doses 1.05 mg and/or 2.1 mg of cisplatin per kg). The highest level of MT at rats treated with 1.05 mg cisplatin was determined after four hours as 4.9 μmol/L. In the case of the second experimental group the maximum was reached even after two hours of the treatment as 4.8 μmol/L. In addition we were interested in the effect of cisplatin or carboplatin treatment of patients with a tumor disease. At patients with tumor in head and neck area treated with cisplatin we observed that the level of MT was going higher due to administration of the drug. This phenomenon was observed at all patients. However at patients with retinoblastoma treated with carboplatin we observed various phenomena including decreasing, increasing or no changes in MT level. Progression of MT levels was therefore individual and probably depended on tumor resistance to carboplatin.