The effect of heavy metals on the degradation of dibenzofuran by Sphingomonas wittichii RW1 was determined in liquid cultures. The results showed that 10mg/L cadmium, mercury and copper not only affected the growth of RW1 with dibenzofuran but also the ability of resting cells to degrade this compound. Growth and degradation were strongly inhibited by mercury, even at 1mg/L, while the inhibitory effect of cadmium and copper at the same concentration or at 5mg/L were negligible. In contrast, arsenic and lead did not affect degradation or growth, even at very high concentrations of 100mg/L. Subsequent analyses additionally revealed that concentrations of arsenic and lead remained unchanged following incubation, while those of cadmium, mercury and copper decreased significantly.