Uptake of the mosquito larvicide temefos (Abate) by the salt march snail (Melampus bidentatus Say) in New Jersey was measured by gas-chromatographic analysis. Measurable quantities of temefos were found in the snails within 1 day after the first treatment with a 2% granular formulation but 3 weeks elapsed before uptake occurred following treatment with a temefos emulsion. Residues in the snails exposed to the granular formulation were generally more than 10 times higher than those in snails exposed to the emulsion although application rates of the granular formulation were only about three times higher than those of the emulsion. Residues in snails exposed to the emulsion fell below detectable levels less than 3 weeks after cessation of treatments although measurable amounts were found in snails exposed to the granular formulation for more than 5 weeks after the last treatment. The persistence of temefos in M. bidentatus suggests the potential for its movement through food webs exposed to the granular formulation.