In this study, we have examined the spatiotemporal distribution of the 1 integrin subunit, a putative laminin and collagen receptor, in avian embryos, using immunofluorescence microscopy and immunoblotting techniques. We used an antibody raised against a gizzard 175 × 10³M_r membrane protein which was described previously and which we found to be immunologically identical to the chicken α1 integrin subunit. In adult avian tissues, α1 integrin exhibited a very restricted pattern of expression; it was detected only in smooth muscle and in capillary endothelial cells. In the developing embryo, α1 integrin subunit expression was discovered in addition to smooth muscle and capillary endothelial cells, transiently, in both central and peripheral nervous systems and in striated muscles, in association with laminin and collagen IV. α1 integrin was practically absent from most epithelial tissues, including the liver, pancreas and kidney tubules, and was weakly expressed by tissues that were not associated with laminin and collagen IV. In the nervous system, 1 integrin subunit expression occurred predominantly at the time of early neuronal differentiation. During skeletal muscle development, α1 integrin was expressed on myogenic precursors, during myoblast migration, and in differentiating myotubes. α1 integrin disappeared from skeletal muscle cells as they became contractile. In visceral and vascular smooth muscles, α1 integrin appeared specifically during early smooth muscle cell differentiation and, later, was permanently expressed after cell maturation. These results indicate that (i) the expression pattern of α1 integrin is consistent with a function as a laminin/collagen IV receptor; (ii) during avian development, expression of the α1 integrin subunit is spatially and temporally regulated; (iii) during myogenesis and neurogenesis, expression of α1 integrin is transient and correlates with cell migration and differentiation.