Laboratory studies were made to determine the fate of 14C-labeled aldicarb in sand, loam, day, and muck soils maintained at different moisture levels of 0, 50, and 100% of field capacity and at pH values of 6, 7, and 8. For the most part, no important differences could be attributed to pH within the range used. Aldicarb was relatively stable in all dry soils, in sand at all moisture levels, and in loam with 50% moisture; the half-life of all toxic compounds exceeded 56 days. A moisture level of 50% was optimum for the oxidation of aldicarb to its toxic sulfoxide and sulfone derivatives in loam, clay, and muck, and a moisture level of 100% caused a substantially faster rate of decomposition to nontoxic products in the same soils. Other laboratory studies with 35S-labeled aldicarb demonstrated that the volatilization of aldicarb and its derivatives was influenced greatly by soil moisture; as the rate of the evaporation of water increased, so did volatilization of radioactivity from treated soil. Field studies were conducted with loam and sand soils that were treated with 35S-labeled aldicarb, confined in packets made of stainless-steel screen, and buried in a cotton field, where they were exposed to wet or dry conditions. Under extremely wet conditions, all radioactivity was lost from the packets in a matter of hours. Under dry conditions, the half-lives of the toxic compounds were 1 day in sand and 4-7 days in loam.