Plasma concentrations of morphine (MOR), morphine-3-glucuronare (M3G) and morphine-6-glucuronare (M6G) were analyzed in 3 renal dysfunction patients who had received morphine. The patients showed increased plasma concentrations of MOR, and marked increases in M3G and M6G. These results indicare that MOR metabolites accumulate in plasma more easily than MOR itself in advanced cancer-related pain patients with renal dysfunction. In cancer patients with renal dysfunction, assessment of plasma concentrations of MOR and MOR metabolites is necessary determine the optimal MOR doses.