Significant amounts of the urinary metabolity p-nitrophenol were detected in the urine of sprayment as long as ten days after last exposure to the organophosphorus insecticide, parathion. Approximately two days after exposure, excretion was insignificant during late night and early morning hours, but reached higher levels during midday. The height of immediate postexposure excretory peaks and the delayed midday rises in excretion seemed to vary directly with the temperature. Bathing after exposure was associated with a rapid decrease in p-nitrophenol excretion. Tests considering only one route of exposure at a time indicated that the dermal route represents a potentially greater source of absorption than the respiratory route for orchard spraymen using liquid parathion formulations under the conditions of this study. However, with equivalent absorbed dosages the respiratory route is the more hazardous.