CaO2 was optionally modified by addn. of urea and phosphates and then used for enhancement of biodegrdn. of polycyclic arom. hydrocarbons (PAH) in soil permanently polluted with petroleum. The CaO2 treatment of microflora-contg. soil resulted in an increase in PAH removal by biodegrdn. up to 58% for anthracene, 66% for fluoranthene, 80% for pyrene ang 96% for chryzene.