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Summary Mouse alloantigen Ly‐6.2 is detectable in various non‐lymphoid tissues such as kidney, but it is not clear whether or not this expression is due to bone‐marrow derived passenger leukocytes. To determine whether non‐marrow derived cells express Ly‐6.2, we examined the expression of this antigen in kidney and on isolated connective tissue and epidermal cells. Studies in radiation chimeras demonstrated that the kidney did not become Ly‐6.2 positive when negative animals were reconstituted with positive marrow. Thus, passenger leukocytes cannot account for the renal expression of Ly‐6.2, indicating that most of this antigen is on non‐marrow‐derived (parenchymal) cells in kidney. Various isolated cell types‐fibroblasts, osteocytes, chondrocytes and skin epidermal cells‐were found to be Ly‐6.2 positive. Indeed, absorption and cytotoxicity results suggested that the amount of Ly‐6.2 on fibroblasts exceeded the amount of an H‐2 antigen on these cells. Comparison of fibroblast to lymphocytes indicated that fibroblastts had 13‐60 times more Ly‐6.2 than spleen cells and three times more than PHA blasts. The results indicate that the Ly‐6.2 detected in non‐lymphoid tissues is predominantly on the parenchymal or connective tissue elements of those tissues.