A mathematical model was developed to integrate the physical concepts needed to predict the concentration of tebuthiuron in runoff and soil water. The model is based on a mass balance equation combined with a hydraulic routing equation and a solute transport equation in soil water. These equations are linked by a diffusion-controlled release of solutes from soil water to runoff. Field experiments were conducted on the Walnut Gulch Experimental Watershed in southeastern Arizona. A rotating-boom rainfall simulator was used to apply simulated rainfall to paired 3 x 11 m plots. The model was tested using rainfall simulator data after the application of tebuthiuron on a dry and on a wet soil. Rainfall, runoff, sediment and soil moisture content were sampled along with tebuthiuron concentration in soil, runoff and sediment. The results showed that the model represented the observations found in the field, though tebuthiuron concentrations in runoff were overestimated in the early stages of the runoff events.