A new lightning return stroke model is proposed in which the lightning channel, previously charged by the leader, is exponentially discharged with the discharge time constant being a general function of height. The new model is both more general and more physically reasonable than the Diendorfer-Uman model (Diendorfer and Uman, 1990) and its modification by Thottappillil et al. (1991). In the new model a single height-variable discharge time constant is used instead of the two height-invariant discharge time constants used for natural lightning in the Diendorfer-Uman model. As an illustration of the use of the new model, the measured electric fields for three triggered lightning return strokes about 5-km distant are compared with the fields calculated from the model, using simultaneously measured channel base current and return stroke speed as inputs to the model. ¿ American Geophysical Union 1994