N-isopropyl-p-I-123-iodoamphetamine (123I-IMP) is extracted by the brain in proportion to regional blood flow. It is particularly useful in the clinical assessment of various pathological conditions related to altered cerebral flow. Moreover, it has been reported that 123I-IMP is avidly incorporated into melanin and melanotic melanoma. We evaluated 123I-IMP scintigraphy using either planar or single photon emission tomography (SPET) studies in 10 patients with malignant melanoma. The patients were classified into two groups according to the tumour site: Group A, six patients with primary or metastatic cutaneous malignant melanoma of the extremity with planar scintigraphy; Group B, four patients with primary malignant melanoma of other organs with planar scintigraphy and SPET. In Group A, tumour uptake was demonstrated in four of six patients; in Group B, three of four patients had tumour accumulation on SPET and planar scintigraphy. SPET revealed the exact tumour localization, even in the case of a tumour located in the lung. These results suggest that planar scintigraphy using 123I-IMP is useful in the detection of malignant melanoma. Furthermore, more clear tumour localization is possible with SPET, even in the case of a tumour located in the lung.