A1As(y)Sb(1-y) and InAsySb1-y ternaries have been grown by Molecular Beam Epitaxy on (001) GaAs and (001) InAs substrates. Growth parameters and composition of the layers were determined by reflection high-energy electron diffraction and single-crystal X-ray diffraction measurements, respectively. The compositional dependence of AlAsySb1-y and InAsySb1-y on the ratio of Sb-4 to As-2 (or As,) fluxes as well as on the substrate temperature has been investigated and can be explained qualitatively. The 'smoothing' effect of Sb during the growth has been observed. (C) 1998 Elsevier Science S.A.