Bis (methylmercuric) selenide (BMS) formed in the blood, liver, kidney and brain of rat simultaneously injected with methylmercury and selenite was extracted by use of two methods (Method I and II). In the case of Method I, the tissue was homogenized in 15 mM phosphate buffer (pH 7.4) in a high speed high power homogenizer and then BMS was repeatedly extracted 8 times with benzene from the homogenate. In the case of Method II, the tissue was ground in benzene in the same homogenizer and then BMS was repeatedly extracted 8 times with benzene from the ground tissue. BMS was recovered very insufficiently when it was extracted from the blood, liver, kidney and brain by the single extraction of Method I. It was found that the larger amount of BMS was recovered from all tissues by the fewer extraction procedures when Method II was used in the place of Method I. In the case of the liver or kidney, the recovery amount of BMS in Method I was about 60% of that in Method II. These results suggest the possibility that Method II is superior to Method I as an extraction method of BMS in animal tissues.