The distribution of the microtubule-associated protein MAP2 in cultured hippocampal neurons was studied using immunocytochemistry with monoclonal antibodies. MAP2 was preferentially localized to dendritic, but not axonal, processes even in single isolated cells which developed without making intercellular contacts. Hence regional differences in the molecular composition of the neuronal cytoskeleton can develop independently of cell interactions. The presence of MAP2 may be a useful marker for identifying dendrites in cell culture.