The aim of our study was to examine whether technetium-99m 1,2-bis[bis(2-ethoxyethyl) phosphino]ethane (tetrofosmin) a lipophilic, cationic tracer which was first developed for myocardial perfusion imaging, could be a new radiopharmaceutical for melanoma imaging. We therefore used two human cell lines, SK-MEL 28 and 5i8 A2 (n = 6, cell concentration 106/ml, incubation at 22 degrees C and 37 degrees C, 50-100 approximately lCi/ml Tc-99m-tetrofosmin, time of incubation 10-180 minutes). The cellular uptake by both cell lines was determined. In contrast to another non- melanoma tumor cell line MCF-7 (a human adenocarcinoma breast cancer) which reached steadystate almost immediately (within 10 minutes), the cellular uptake of SK-MEL-28 increased after 60 minutes and showed a very high uptake (> 10%) after 120 minutes and decreased after 180 minutes (6-8%), while the uptake in 518 A2 cells was about 5% after 90 minutes. Our data show that Tc-99m-tetrofosmin could be a promising agent for melanoma imaging.