Gd-155 Mossbauer spectroscopic studies of the title complexes have been performed. Although the Gd-155 isomer shifts (delta) varied scarcely, the quadrupole coupling constants (e(2)qQ) changed in the range 4.07-4.81 mm s(-1). The e(2)qQ values of KGdM(CN)(6) . 3H(2)O (M = Fe-II and Ru-II) are larger than those of GdM(CN)(6) . 4H(2)O (M = Cr-III, Fe-III, and Co-III), these values increasing with increasing orthorhombic distortion of the crystal structures. A relationship between the e(2)qQ values and the ionic radii of the transition metal ions has also been recognized.