This paper reports two related studies of the Form II --> Form I crystal-crystal transformation in isotactic polybutene-1. First, it was found that in melt spun filaments, the rate of transformation is higher in filaments possessing higher levels of crystalline orientation. Second, we consider the occurrence of this phase transformation in thick quenched cylindrical rods. It was found that the phase transformation occurs more rapidly in the core than at the surface of the part. It is hypothesized that the mechanism of the higher transformation rate in the core is due to the development of residual quench stresses associated with densification at solidification. These stress levels have been calculated and our results compared with earlier studies.