Compression-molded polypropylene samples, pre-annealed at 135°C, were quenched from 120-123°C and stored at 23°C in an inert atmosphere in the dark. Thermal expansivity, 1-Hz dynamic modulus and damping, small-strain creep compliance, tensile stress strain diagrams and notched and unnotched Charpy impact strength were measured as functions of temperature on samples stored (aged) at 23°C for periods ranging from 0 to 6,000 h. Quite substantial aging effects were detected. The aging effects are similar to those found in amorphous polymers; a possible explanation, not based on secondary crystallization, is discussed. -- AATA