Neurofilament protein and calcium-binding proteins parvalbumin, calbindin, and calretinin are present in morphologically distinct neuronal subpopulations in the mammalian cerebral cortex. Immunohistochemical studies of the hippocampal formation and neocortex have demonstrated that while neurofilament protein and calbindin are localized in subsets of pyramidal neurons, the three calcium-binding proteins are useful markers to differentiate non-overlapping populations of interneurons. To date, most studies have been performed in rodents and primates. In the present analysis, we analyzed the distribution of these proteins in the canine hippocampus. Neurofilament protein was present in large multipolar neurons in the hilus and in pyramidal neurons in the CA3 field, whereas pyramidal neurons in the CA1 field and subiculum were less intensely immunoreactive. Parvalbumin immunoreactivity was observed in large multipolar neurons in the hilus and throughout the CA3-CA1 fields, in a few pyramidal-shaped neurons in the CA1 field and subiculum, and had a distinct neuropil staining pattern in the granule cell layer and stratum pyramidale of the Ammon's horn. Calbindin immunoreactivity displayed a strong labeling of the granule cells and mossy fibers and was also observed in a population of moderately immunoreactive neurons in the CA1 field and subiculum. Calretinin immunoreactivity was relatively weaker overall. The inner molecular layer in the dentate gyrus had a distinct band of labeling, the stratum lacunosum/moleculare contained a punctate neuropil staining, and there were a few small multipolar neurons in the hilus, CA3-CA1 fields, and subiculum. Comparison of the staining patterns observed in the dog hippocampus with those in human, macaque monkeys and rats revealed that although there are some subregional differences among these taxa, the dog may constitute a valuable large animal model for the study of certain neurological conditions that affect humans, in spite of the phylogenetic distance between carnivores and primates.