I.r. spectral and X-ray diffraction studies were carried out on the methyl ester of dithiocarbazic acid, NH2·NH·C(:S)-SMe (I), and of its N-substituted derivatives. NMe2·NH·C(:S)SMe (II), and NH2·NMe·C(:S)SMe (III). Crystals of (I) are monoclinic, space group C2/c, Z= 8, unit cell dimensions: a= 14.018(5), b= 5.518(3), c= 14.079(4)Å, β= 98.4(1)°; (II) monoclinic, space group P21/c, Z= 4, unit cell dimensions: a= 8.487(8), b= 9.920(9), c= 10.611(9)Å, β= 117.1(1)°; (III), monoclinic, space group P21/c, Z= 4, unit cell dimensions: a= 7.071(5), b= 9.815(6), c= 10.142(7)Å, β= 114.0(1)°. The structures were solved from diffractometer data by Patterson and Fourier methods and refined by block-diagonal least squares to R 0.028 (I). 0.036 (II), and 0.029 (III) for 1 256, 1 132, and 917 reflections. The basic units of these structures are centrosymmetric dimers formed by NH N hvdroaen bonds in (I), and by N–H S hydrogen bonds in (II) and (III). The component monomers are in the cis, trans-conformation, i.e. with the group–NH·NH2 bent toward C–S and the SMe towards the opposite side in (I) and in the trans, cis-conformation in (II) and (III). Change of conformation or of substituents does not significantly alter bond distances in the molecules.