Small amounts of a reactive terpolymer added to a binary blend of polyamides and thermotropic liquid crystalline polyesters prior to injection moulding yielded in situ composites with significantly higher modulus and strength along the machine/reinforcement direction and substantially higher strength and toughness along the transverse direction of injection moulded parts. These were attributed to enhanced fibrillation of the liquid crystalline polymer (with fibril formation observed along the core regions of injection moulded parts also) when injection moulded in the presence of the terpolymer and improved interfacial adhesion characteristics between the components of the in situ composite. Finally, in situ composites injection moulded in the presence of the terpolymer displayed smoother surfaces.