Three types of com. petroleum bitumens were modified with atactic polypropylene (APP) and low-d. polyethylene (PE). The blends were exposed to weather conditions for 1 year to study their ageing and then the changes of their properties. The addn. of APP resulted in an increase in softening temps. without any substantial changes of other blend properties. The addn. of PE film resulted in an increase in both softening and fragility temps. and in a considerable decrease in the penetration and ductility of the blends. The addn. of polymers did not affect the course of bitumen ageing.