AbstractCells interact with the extracellular matrix through receptors, most commonly of the integrin family. We (Cachaço et al. [] Development 130:1659–1671) and others (Schwander et al. [] Dev. Cell 4:673–685) have demonstrated a role for β1 integrins in mouse primary myogenesis. However, it is unclear what α subunits pair with β1 during this process in vivo. Here, we determined α subunit expression patterns at embryonic day (E) 11.5–E14.5. Differentiated myotomal myocytes express all α subunits studied. As the muscle masses form both in trunk (E12.5) and limbs (E11.5–E12.5), laminin receptors α6β1 and α7β1 are undetectable, and an assembled laminin matrix is absent. Instead α1β1, α4β1, α5β1, and an αv‐containing integrin are expressed and unassembled laminin and fibronectin are abundant around myogenic cells. At E13.5–E14.5, α6β1 and α7β1 are expressed, and a laminin matrix forms around individual myotubes. Thus, myogenic cells change their integrin expression pattern during the course of primary myogenesis in the mouse, suggesting different roles for fibronectin‐ and laminin‐containing matrices in this process. Developmental Dynamics 232:1069–1078, 2005. © 2005 Wiley‐Liss, Inc.