INTRODUCTION Biomolecules having the general formula GXAsR2 have been the subject of a num- ber of studies during the past seven years. In these compounds, X is S or Se and derivatives have been prepared in which G is a monosaccharidela or an amino acid or di- or tripeptidelb. At the present, 22 of these derivatives have been found to be active ( % T/C - 125) against mouse leukemias in in vivo testing (PS388 and L1210 test systems). These ...