Insecticide use on cotton has shifted away from the organochlorine compounds toward the organophosphate, carbamate and pyrethroid compounds. These latter three groups of compounds are generally less environmentally persistent and frequently more selective than the organochlorine compounds. However, the conventional emulsifiable concentrate (e.c.) formulations of the organophosphates, methyl parathion (MP) and ethyl parathion (EP) are extremely hazardous for the applicator and other field workers. Because of the limited residual insecticidal activity of the e.c. formulations of MP and EP, repeat applications at 3 or 4 day intervals are frequently necessary for effective insect control (Louisiana Cooperative Extension Service 1985). Microencapsulated (encaps.) formulations of MP (Penncap-M) and EP (Penncap-E) are now available and have been reported to provide extended persistence on tobacco (Leidy et al. 1977) and peach trees (Winterlin et al. 1975), reduced volatilization to the atmosphere (Jackson and Lewis 1979) and reduced mammalian toxicity with increased user safety (Ivy 1972). However, Pass and Dorough (1973) reported that e.c. and encaps, formulations of MP gave equal weevil control in alfalfa and that the dissipation rates of the two MP formulations were the same. The present study was undertaken to compare the persistence of MP and EP, applied as e.c. and encaps, formulations, on cotton foliage under field conditions in the Mid-South. This paper presents the results of research only. Mention of a pesticide does not constitute a recommendation for use by the U.S. Dept. of Agriculture nor does it imply registration under FIFRA as amended. Names of products are included for the benefit of the reader and do not imply endorsement or preferential treatment by the U. S. Dept. of Agriculture.