The profiles of major metabolites of primaquine (PQ) produced from liver microsomal (MC) and mitochondrial (MT) metabolism were investigated in vitro by silica gel thin layer and reverse phase high pressure liquid chromatography (HPLC). The results indicated that 5-hydroxy primaquine (5-OH PQ) and carboxyprimaquine (CPQ) were simultaneously produced by either microsomes or pure mitochondria preparations. However, the quantitative study showed that microsomes produced approximately 19 times more 5-OH PQ but only 1/34 of the CPQ by mitochondria.