Tensile strains have been determined as a function of time for polypropylene during (a) two-step loading, (b) creep recovery following removal of a load, and (c) intermittent load application. Data are presented at 23 degrees C for specimens of different physical age, for different stress levels in the non-linear range and various durations of loading. The results are compared with predictions based on a pseudo-linear model. They have also been analysed using a modified superposition procedure that allows for changes in mean retardation time due both to physical ageing and to the application and removal of loads. This analysis has provided useful information on the variations of molecular mobility during the different loading histories. The functions and associated parameters used in the analyses could also form the basis of a method for presenting design data on plastics. Crown