There have been previous reports of somatostatin- and acetylcholinesterase (AChE)-positive patches in the superficial layers of the presubiculum in monkeys. In this study, we show additional instances of patches in the presubiculum, as demonstrated by cytochrome oxidase (CO), by myelin and Nissl stains, and by the calcium-binding proteins calbindin (CB), calretinin (CR), and parvalbumin (PV). Markers are differentially expressed along the lateral and longitudinal axes. Comparisons of adjacent sections reacted for different markers suggest that the CB+ and CR+ patches, and CO+ and AChE+ patches generally correspond, but not the CB+ and CO+ patches. In cross section, patches are about 100-300 microm in width. Sections cut tangentially through the superficial layers indicate that the pattern of CO and AChE labeling is in fact patchlike in layer I, but that the apparent patches in layer II (CB and CR) form a reticular or lattice-like network. As patches are restricted to the presubiculum, these labeling patterns provide a convenient marker for the boundary between the presubiculum and the adjoining posteroventral retrosplenial cortex. More work is necessary to determine how this modularity may relate to the functional organization of the presubiculum.