AbstractWe have examined the immunolocalization of β1‐integrin during feather development in the spino‐lumbar tract of the backskin from normal and scaleless chick embryos. β1‐integrin appears during early feather development in three distinct phases which correspond to important developmental events. The first phase (5–5½ days of incubation; Hamburger and Hamilton [H.H.] stage 27) represents the period prior to the formation of dermis. During this phase, β1‐integrin antiserum labels mesenchymal cells located in the central region of the spino‐lumbar tract where the initiation site for feather development is located. The second phase (5½–7½ days of incubation; H.H. stages 28–32) corresponds to the period during which dermis is formed. The cells that make up the dermis are readily distinguished by their lack of β1‐integrin immunostaining. The third phase (7½–10 days of incubation; H.H. stages 33–36) begins with the sudden appearance of β1‐integrin in the central and lateral regions of the dermis. The pattern of β1‐integrin immunostaining in scaleless backskin becomes different from that of normal backskin during this phase. In normal backskin the dermal condensations of feather germs are not labeled with the β1‐integrin antiserum. This produces a heterogeneous immunostaining pattern very similar to the pattern seen for Type I collagen (Mauger et al. [1982] Dev. Biol. 94:93–105). In contrast, homogeneous immunostaining is observed in the dermis of scaleless backskin. The initial time of appearance, manner of appearance, and pattern of integrin expression in the third phase suggest that β1‐integrin may be involved in the stabilization of the feather pattern.We also observed the appearance of β1‐integrin on the epidermal basal cells during the time of feather follicle formation. The β1‐integrin antiserum reacts strongly with the baso‐lateral surfaces of normal basal cells, yet the basal surfaces of the scaleless basal cells are unstained. This lack of immunostaining along the basal surfaces of the scaleless basal cells may relate to the abnormal adhesion between the epidermis and dermis in scaleless backskin. © 1994 Wiley‐Liss, Inc.