The urinary excretion of p-nitrophenol and of dichlorodiphenylacetic acid (DDA) was measured in spraymen applying formulations containing both parathion and DDT. In each instance, excretory level of metabolite correlated well with exposure to the pesticide. Para-nitrophenol excretion levels showed changes of greater magnitude in response to a specific exposure than did DDA excreation. However, in general the excretory patterns for p-nitrophenol and DDA were similar. Both metabolites reached peak levels at about the same time interval (p-nitrophenol, 8.7 hours; DDA, 10.1 hours) after exposure began. Excretion of both p-nitrophenol and DDA tended to increase with an increase in ambient temperature. Excretion curves for both metabolites showed diurnal variation during the period after exposure had ended. On the average for a specific exposure, more parathion-derived material than DDT-derived material was recovered in the urine.