The half-life of the insecticide acephate and its hydrolysate, methamidophos, in the rind of Temple and Valencia oranges, and grapefruit, lemons and tangerines was 10.3 and 10.5 days, respectively. Half-lives of acephate and methamidophos in citrus pulp were 15.0 and 6.1 days, respectively, based on 7, 14 and 21 day data. Seven days after treatment, acephate and methamidophos reached maximum levels in rind and pulp. Acephate residue levels in rind were less than 3.0 ppm 14 days after treatment; acephate residues in pulp were less than 3.0 ppm throughout the experiment. Methamidophos residue levels averaged less than 0.25 ppm after 21 days.