Mushroom (Shiitake) grown on wood (Kashi) was exposed to mercury vapor and the mercury uptake was measured. With lapse of time, mushroom (Shiitake) took up metallic mercury at the plait of the cap and this increased daily. After about ten days, it reached a level of 4.5 μg/g, at which it remained constant. Shiitake crude extract took up mercury. Catalase and peroxidase inhibitor Potassium cyanide (KCN), Sodium azide (NaN(3)) and specific catalase inhibitor 3-Amino-1,2,4 Triazole (AT) inhibited mercury uptake respectively. Crude Shiitake extract without hydrogen peroxide (H(2)O(2)) showed a 53% decrease with H(2)O(2), and with H(2)O(2) plus KCN a 47% (5mM KCN), a 60% (10mM KCN), a 65% (20mM KCN) decrease occurred with H(2)O(2), in regard to the ability to take up mercury from air saturated with mercury vapor. Shiitake crude extract with H(2)O(2) plus NaN(3) inhibited mercury uptake almost completely, and with L-Ascorbic acid (VC) plus AT a 72% (5mM AT), a 89% (10mM AT), a 90% (20mM AT) decrease occurred, and with H(2)O(2) plus VC plus AT a 77% (5mM AT), a 90% (10mM AT), a 90% (20mM AT) decrease occurred. 3-Amino-1,2,4 Triazole, a specific catalase inhibitor, inhibited catalase activity and mercury uptake. This showed that Shiitake crude extract takes up mercury from air saturated with mercury vapor by hydrogen peroxide and catalase.