Cisplatin (CDDP) was microencapsulated with ethylcellulose, and microcapsules (CDDP-mc) were infused into the maxillary arteries of patients with various head and neck carcinomas. We then found that the CDDP level in the circulating blood was significantly lower than that in patients administrated intravenous non-excapsulated CDDP. However, significantly high concentrations of CDDP were found in the tissues of patients treated with CDDP-mc. Our results suggest that selective arterial infusions of CDDP-mc can exert an intensive topical antitumor effect through microinfarction of malignant tissues. The prolonged release of drug from the microcapsules has also been associated with minimal systemic side effects.