The stability of heavy metal sulfides (MnS, FeS, ZnS, CuS, and HgS tagged with35S) in aerobic and anaerobic soil was studied. The sulfides are listed in decreasing order of solubility. Water extracts of each treated soil were made regularly during a 75-day incubation period. The radioactivity of the extracts was indicative of the stability of the water-soluble salts. For the aerobic soils, H2O-extractable35S decreased with a decrease in solubility of the sulfide. The metal-sulfides were relatively stable in the anaerobic soil. The least soluble salt was the most stable.To study the oxidative capacity of rice (Oryza sativa L.) roots the35S tagged metalsulfides were mixed with anaerobic soil to which rice was transplanted. The tagged soil was placed in the lower rooting zone and covered to a depth of 8 cm with unlabeled soil. The transplanted rice plants were grown for specific times and the aerial portions harvested. The uptake of35S from the respective sulfide salt was determined. The apparent degree of stability and subsequent uptake of35S was directly related to the solubility of the sulfide salt. No35S was taken up from the Hg35S.