In a wood processing factory, the measured air concentration of birchen dust was 1. 26 ±0. 41 mg/m3, and the micronucleus frequency of peripheral blood lymphocytes in 83 workersexposed to wood dust was 1. 13 ± 2. 83%, which was significantly higher (P < 0.01 ) thanthat of control group (0. 51 ± 1. 41% ). The number of exposed workers with positive mi-cronucleus test was 9. 6 %, which was higher than that of control group (4. 5 % ), but thedifference was not significant (P >0. 05 ). The micronucleus test in mice treated with waterextracts of unsteamed and unbaked birchen dust showed that the micronucleus frequencies inall treated groups were significantly higher than that of contro group (P < 0. 01 ) and therewas also a doseresponse correlation (r = 0. 96, P < 0. 0005 ). The results of steamed andbaked birchen dust extracts were significantly lower than those of the unsteamed and unbakedones at the same doses (P< 0. 001 ). This suggests that when the birchen dust is steamed atthe temperature of 100℃ for 24h or baked at the temperature of 80℃, its inducing effect inmicronucleus test could be lowered In a wood processing factory, the measured air concentration of birchen dust was 1. 26 ± 0. 41 mg / m3, and the micronucleus frequency of peripheral blood lymphocytes in 83 workersexposed to wood dust was 1. 13 ± 2.83%, which The number of exposed workers with positive mi-cronucleus test was 9. 6%, which was higher than that of control group (4), was significantly higher (P <0.01) thanthat of control group (0. 51 ± 1. 41% . 5%), but the difference was not significant (P> 0.05). The micronucleus test in mice treated with waterextracts of unsteamed and unbaked birchen dust showed that the micronucleus frequencies inall treated groups were significantly higher than that of contro group (P <0. 01) and therewas also a doseresponse correlation (r = 0.96, P <0.0005). The results of steamed and baked birchen dust extracts were significantly lower than those of the unsteamed and unbakedones at the same doses (P < 0. 001). This suggests that when the birchen dust is steamed atthe tem perature of 100 ℃ for 24h or baked at the temperature of 80 ℃, its inducing effect inmicronucleus test could be lowered