We found that R-cadherin, a Ca2(+)-dependent cell--cell adhesion molecule, is expressed in restricted regions of the mouse fetal brain, as was found for E-cadherin previously. R-cadherin delineated a subset of alar domains within forebrain neuromeres and certain future nuclei, while E-cadherin was expressed in another distinctive pattern. When cells were collected from various local regions of the fetal brain, dissociated, and reaggregated under the conditions in which only cadherins are active for cell aggregation, R-cadherin-positive and -negative cells segregated from one another. Similar results were obtained for E-cadherin. Such segregation of cells was, however, suppressed when the cadherins were inactivated either by Ca2+ depletion or with blocking antibodies. These results suggest that cadherins confer region-specific adhesiveness on fetal brain cells and that this process may take part in brain segmentation.