A new method for the activity measurement of 115mCd in biological samples was proposed. After tissues mineralization with 60% perchloric acid and 30% hydrogen peroxide (I) or with 0.5 M ethanolic sodium hydroxide (II) the solutions were measured in automatic liquid scintillation counter SL-30 by CERENKOV technique. The channels ratio method was successfully applied for standardization. The recoveries of 115mCd varied in the ranges: 93.6-102% and 82.7-99.3% for method I and II, respectively.