An alternative approach was presented for estimating annual toxic contaminant loadings in urban runoff. In this method, the mean contaminant concentrations are calculated by a regression method. In the computation of contaminant loadings, the load component transported by the liquid phase was estimated by multiplying the mean concentration in water by the runoff volume simulated by the STORM model. The load component transported by suspended solids was calculated by multiplying the mean concentration in solids by the event mean solids concentrations reported in the NURP Program. The loadings calculated by this method were compared with those obtained from whole water samples, and the differences are within an order of magnitude. Since more parameters are used in this approach, it appears more suitable for use in sensitivity analysis of parameters, and more flexible in evaluations of controls measures.