The tensile and shear moduli of four thermoplastic composites are deter mined using three-point beam flex tests at different spans. The experimental values are compared to the predictions of the rule of mixtures and the rule of mixtures modified by the stress partitioning function. Tensile and flexure strengths are also determined. The results are compared to data for a thermoset composite. The measured shear moduli of thermoplastic composites is lower than that predicted when a stress partitioning function of .4 is used. Laminates with large areas of voids had lower shear moduli, and lower ten sile and flexure strength than void-free laminates.