LPE growth of quaternary Ga1-xAlxAsySb1-y, and Ga1-xInAsySb1-y compounds on (100) GaSb substrates has been investigated for growth temperatures T-o = 590-594 degreesC and various amount of supersaturation. Epilayers were characterised by means of XRD, TEM, AFM, EPXMA and SIMS. It has been found that LPE growth at T-o similar to593 degreesC produces good quality single Ga1-xAlxAsySb1-y layers unless the Al content in the melt does not exceed x(Al)(1) = 0.02 giving perfectly matched Ga1-xAlxAsySb1-y epilayers with Al content in the solid up to x = 0.03. Also, smooth and lattice matched Ga1-xInxAsySb1-y layers for indium atomic fraction in liquid up to x(In)(1) = 0.40 have been grown. For higher In content in the melt quality of layers drops drastically because corresponding composition of such layers are situated near miscibility gap. Our approach to fabrication epilayers with high value of x relies on the use of an additional inter-layer GaAlAsSb, lattice-matched to GaSb, inserted between GaSb and high x index epitaxial layer. With such a procedure we were able to grow smooth and homogeneous Ga1-xAlxAsySb1-y epilayers; with Al content in solid x = 0.62 and Ga(1-x)ln(x)As(y)Sb(1-y) layers with In content of 0.24. (C) 2003 Elsevier B.V. All rights reserved.