Semi-insulating plates made from CdTe i Cd1-xZnxTe are currently used for preparing X and gamma radiation detectors. For many years there has been a search for another semiconductor based on CdTe, suitable for making large, monocrystalline, semi-insulating, and homogeneous detector plates. Recently, a series of investigations has been devoted to a possibility of using crystals based on CdTe with addition of magnesium (Mg), or selenium (Se) for X and gamma radiation detectors. In our previous paper [1] we presented results of investigation of CdTe with magnesium: Cd-1 _ xMgxTe. In this paper we present results of investigation of crystals CdTe with selenium (Se) and with both selenium and manganese (Mn): CdTe1 _(x)Se(x )and Cd-1 _xMnxTe1 _ Se-y(y) .