R-cadherin was originally identified as a chicken cadherin expressed by the retina. Here, we describe the identification of a mouse homologue of R-cadherin. We isolated mouse cDNAs encoding a cadherin with 94% identity in amino acid sequence to the chicken R-cadherin, and defined this molecule as mouse R-cadherin. L cells transfected with the mouse R-cadherin cDNA acquired a cadherin-mediated cell-cell adhesiveness as found for other cadherins. To examine the binding specificity of mouse R-cadherin, L cells expressing this cadherin (mRL) were mixed with L cells expressing chicken R-cadherin (cRL), mouse N-cadherin (mNL), mouse E-cadherin (mEL) and mouse P-cadherin (mPL). While mRL cells randomly intermixed with cRL cells, those cells aggregated separately from mEL or mPL cells. Mixing of mRL with mNL cells gave an intermediate result; that is, they formed both separate and chimeric aggregates, suggesting that R- and N-cadherin can interact with each other although each has a preference to bind to its own type. Similar properties were previously found for chicken R-cadherin. Thus, the cell binding specificity of R-cadherin is entirely conserved between the two species, suggesting a conserved role for this protein in morphogenesis. We also located the mouse R-cadherin gene to chromosome 2.