Systemic injection of curare changes the depth profile of theta rhythm seen in the hippocampus of the freely moving rat. Under curare, dorsoventral microelectrode advancement reveals the presence of a sudden phase reversal and null occurring at the level of the stratum radiatum of CA1. Further advancement reveals the presence of an amplitude peak in the vicinity of the hippocampal fissure. In addition to the change in depth profile, curare alters the relationship between the amplitudes of the two phasereversed components of the theta rhythm. The change in theta rhythm brought about by curare outlasts the paralytic effect of the drug.