The mechanical properties of continuous fibre reinforced metals (CFRMs) are known to be very sensitive to the selection and composition of the metallic matrix; for aluminium based CFRMs, commercial alloys are not suitable for this purpose. In the present study, the chemical composition of the matrix of unidirectionally Altex fibre reinforced aluminium composites was adjusted to meet the requirements previously established for a maximum exploitation of the fibre strengthening potential in CFRMs, particularly accounting for the peculiarities of the aluminosilicate Altex fibre and of the squeeze casting process. It was found that a matrix made from high purity elements based on the ternary Al - Zn - Mg system confers the best tensile strength properties to the CFRM, provided the Zn and Mg additions are tightly controlled to prevent the formation of interfacial intermetallic compounds during processing. The optimum composition was shown to be Al - 6Zn - (0·3 - 0·6)Mg (wt-%); in this case Zn traps the Mg which leads to the formation of fine matrix precipitates indentified as Zn2Mg (η′ phase), thus preventing a deleterious reaction of Mg at the fibre/matrix interface. The resulting composite material (fibre volume fraction ∼54%) does not require additional heat treatment after casting and yields a tensile strength up to 1116 and 257 MPa in the axial and transverse directions respectively. © 2002 IoM Communications Ltd.