A simple theory for predicting the response times of unsaturated and saturated flows on hillslopes, based on kinematic wave equations, is presented. The sensitivity of unsaturated zone lag and time of concentration of the saturated zone to hillslope and soil parameters, antecedent moisture and input rates is examined. It is shown that for many combinations of parameters subsurface response times are too long to be considered as stormflow; but that the combinations of high hydraulic conductivities, shallow soils and wet initial conditions that lead to fast responses are quite reasonable when compared with field studies of subsurface stormflows. It is suggested that the kinematic theory provides a basis for a practically useful predictive model.