The function of the primate hippocampus and related structures was analysed by making recordings from the hippocampus, subiculum, presubiculum, and parahippocampal gyrus in monkeys actively walking in the laboratory. Head direction cells were found in the presubiculum. The firing rate of these cells was a function of the head direction of the monkey, with a response that was typically 10-100 times larger to the best as compared to the opposite direction. The mean half-amplitude width of the tuning of the cells was 76 degrees. The response of head direction cells in the presubiculum was not influenced by the place where the monkey was, there being the same tuning to head direction at different places in a room, and even outside the room. The response of these cells was also independent of the "spatial view" observed by the monkey, and also the position of the eyes in the head. The average information about head direction was 0.64 bits, about place was 0.10 bits, about spatial view was 0.27 bits, and about eye position was 0.04 bits. The cells maintained their tuning for periods of at least several minutes when the view details were obscured or the room was darkened. This representation of head direction could be useful together with the hippocampal spatial view cells and whole body motion cells found in primates in such spatial and memory functions as path integration.