The effect of concentration, temperature, and soil moisture on chlorpyrifos degradation were investigated in an urban Iowa soil. Soil samples were brought into the laboratory for treatment. Formulated Dursban TC at 10, 500 or 1,000 ppm was applied with water to establish soil moisture tensions of 0.03, 0.30 or 3.00 bar. Treatments were then placed in incubation chambers maintained at 20° and 27°C. Temperature did not affect the degradation of chlorpyrifos or mineralization of its primary metabolite, 3,5,6-trichloro-2-pyridinol (TCP). Soil moisture greatly affected mineralization. The highest percent of mineralization occurred in soil maintained near field capacity (0.30 bar) while the lowest percentage occurred in soil maintained under the driest condition (3.0 bar). Concentration had the greatest effect on the degradation of chlorpyrifos to TCP. At higher concentrations of chlorpyrifos applied, the amount of chlorpyrifos remaining was greater. The highest concentration of chlorpyrifos applied (1,000 ppm) had the highest amount of chlorpyrifos remaining and the lowest relative percentage of TCP formed.