In 1978 the U.S. Environmental Protection Agency accepted captan N-(trichloromethyl) thio 4-cyclohexene 1,2-dicarboximide as a possible candidate for rebutable presumption against continued registration. Risk assessment for the use of materials chosen for RPAR include estimates of worker exposure during various agricultural operations. Observations during earlier field studies in the Columbia Basin Irrigation Project, led us to believe that there was considerable use of captan as a fungicide for seed potatoes. During the spring of 1979 the authors undertook a study of the potential for exposure to captan of workers involved with various aspects of potato planting.