Measurement of residual PAH concentrations showed the promoting effect of planting H. annuus on the dissipation of these chemicals from soil (Table 1). The concentrations of anthracene, fluoranthene, pyrene and crysene in planted soils decreased significantly below the levels detected in the unplanted controls after 45 and 90 d. A positive effect of planting on the dissipation of fluorene was only observed after 45 d, and its concentration remained below the detection limit in both planted and unplanted soils after 90 days. The presence of sunflower plants had no significant effect on the dissipation of phenanthrene in any of the sampling periods. The absence of effect may be connected to the higher solubility in water of this compound (1.8 mg L1), as compared with anthracene (0.045 mg L1), fluoranthene (0.206 mg L1), pyrene (0.13 mg L1) and chrysene (1.8$103 mg L1), what may have caused less bioavailability restrictions to biodegradation of phenanthrene. The increased dissipation was reflected in the significantly lower (p 0.05) concentration of total PAHs in planted pots compared to the unplanted controls, which resulted in a 60% additional decrease in the total PAH content in both sampling periods. With the excep- tion of fluorene, extending the experimental period to 90 days did not result in a significantly lower residual concentration of any of the PAHs in the soils. The chemical analysis of major soil charac- teristics (e.g., pH, texture) did not reveal significant differences after planting with sunflowers, with the only difference being found in the content of total organic carbon, which increased in the planted soils from 0.9 to 2.1% after 90 days.