(1) The uptake of metallic mercury by catalase purified from spinach was observed with and without H(2)O(2). Purified catalase solution took metallic mercury up more than crude catalase solution. (2) In comparison with the mercury uptake from air saturated with mercury vapour, crude spinach extract of catalase with H(2)O(2) showed a 38% decrease with H(2)O(2) plus KCN, a 86% decrease with H(2)O(2) plus NaN(3), and a 19% decrease without H(2)O(2). Uptake by purified extract with H(2)O(2) decreased by 47% with H(2)O(2) plus KCN, decreased about 100% with H(2)O(2) Plus NaN(3), and 65% without H(2)O(2) in comparison with the mercury uptake from air saturated with mercury vapour.