Tensile set was studied at low strains on polypropylene, aliphatic polyketone, rubber toughened blends and CaCO3 particle toughened composites. The rubber in the rubber toughened blends had a particle size of 0.7 mu m. The CaCO3 particles had a size of 0.7 mu m and had been coated with stearic acid. Step-cyclic loading was applied in 1% strain incrementals at a strain rate of 10(-2) s(-1). The maximum strain applied was 20%. The temperature of the test bar was studied with an infra-red camera. Pre-yield deformation is normally assumed to take place in a nonlinear elastic manner. However, for polypropylene and polyketone elastoplastic deformation starts at low strains. For PP the onset of tensile set is at very low strains and increases with strain. The tensile set at the yield point was only 50% and at the drawing strain 100%. Polyketone had a similar tensile set development but shifted to slightly higher strains. Here too the tensile set at the yield point was about 50% and at the drawing strain 100%. The temperature of the non yielded material was found to rise in polyketone a 7 degrees C. The rubber toughened blends had at low strains a higher tensile set, but after the yield strain the set was similar to the base polymer. At 5% strain the tensile set increased with rubber content. The sub micron CaCO3 particle toughened composites increased the tensile set too. The tensile set is a simple technique for studying the pre-yield behaviour of multi phase systems.