Assuming that the lightning return stroke transmission-line model is applicable, we derive an expression for the return-stroke magnetic field for an arbitrary return stroke speed and from that expression show that for a return stroke speed equal to the speed of light c the electric and magnetic field waveforms at all points in space and the current waveform are identical. Recent measurements indicate that the electric field and current waveforms are similar for about 100 ns for triggered lightning return strokes, potentially implying that the initial return stroke speed is actually near c for that time, that is, for the bottom 30 m or so of the triggered lightning channel. While for the transmission-line model the current waveform and the total electric field waveform are identical for a return stroke speed of c, we show that each of the three individual components (electrostatic, induction, and radiation) that comprise the total field varies significantly with distance. ¿ 2001 American Geophysical Union