Evidence is presented indicating that channel geometry is a factor in determining the shape of the electric field waveforms radiated by subsequent return strokes in cloud-to-ground lightning. The data consist of 61 subsequent return strokes in both triggered flashes and natural lightning recorded at the NASA Kennedy Space Center during the summer of 1987. In the case of the triggered flashes, the data include the electric field change, the current at the channel base, and video images of the channel. Video images were obtained for about half of the natural flashes. The fine scale structure of the electric field changes radiated by these strokes has been compared during the first 10 μs. In cases where unambiguous identification of the channel could be made from the video recordings, this fine scale structure is similar for return strokes in the same channel and differs significantly for return strokes in different channels. This is true for both natural and triggered flashes. On the other hand, the current waveforms measured at the channel base (available for the triggered flashes) are similar in shape for all strokes, regardless of the channel. Similar results were also obtained for the natural flashes without video images, in which case strokes from the same flash exhibit a greater similarity than do strokes from different flashes (and therefore different channels). ¿ American Geophysical Union 1995