We propose that integrins help to coordinate the diffetentiation of the internal, sarcomeric cytoarchitecture of a muscle fiber with its immediate environment and are essential for correct integration of muscle cells into tissue. We found that integrin a&& accumulated at contact regions of Drosophila embryo cells cultured in D-22 medium on Drosophila laminin. Myotubes formed, but subsequent addition of serum or fibronectin was needed for sarcomere formation: integrin and actin became concentrated at Z-bands; myosin and actin occurred between the Z-bands. This change failed to occur in the multinucleate myotubes derived from integrin pps null myospheroid mutants. In normal embryos/early larvae, integrin was located at Z-bands and at muscle insertions. Myogenesls and Z-bands were defective in myospheroid embryos. Attachment, spreading, and growth of myoblasts and neurons on the laminin substrate utilized different binding proteins and were independent of integrin.