The uptake and retention of ~3H-HPD in.human malignant cells(cell line MGC 80-3,SGC-7901,BEL-7402,Os-732,Detroit-6 and HeLa)and normal fibroblasts were studied by liquid scintillation counting method.The order of cell lines which took up ~3H-HPD after 30 min.incubation were fibroblasts,HeLa, BEL-7402,Detroit-6,SGC-7901,MGC 80-3 and Os-732 respectively according to the amount of ~3H-HPD in cells.Due to the variety in the amount of excretion, however,those cells which retained ~3H-HPD after 24 hours cultivation were Os-732, Detroit-6, BEL-7402,HeLa,SGC-7901,MGC 80-3 and fibroblasts respectively in respect to the ~3H-HPD level in cells.The uptake was reduced by raising extracel- lular pH and lowering temperature as well as adding higher concentration of serum. Our results showed that the ~3H-HPD content in malignant ceils was higher than those in normal ones and it was because that malignant cells retained ~3H-HPD longer other than took up more