Proliferating skeletal myoblasts show multiple specific responses to laminin, one of the major glycoprotein components of basement membranes. Using MM14Dy myoblasts, a myogenic cell strain derived from a normal adult mouse skeletal muscle, we show in this study that substrate-bound laminin but not other matrix proteins such as collagens or fibronectin specifically and rapidly induces the outgrowth of cell processes, resulting in bipolar, spindle-shaped cells. This effect is independent from the presence of collagens or serum, and was also observed in primary cultures of fetal mouse skeletal myoblasts. The outgrowth of cell processes on laminin is associated with a dramatic stimulation of cell motility: MM14 myoblasts migrate about five times faster on laminin than on fibronectin. In another series of experiments the effect of laminin and fibronectin on thymidine uptake and proliferation of myoblasts was tested. On top of a type I collagen substrate which was provided to ensure complete adhesion even at low doses of laminin or fibronectin, laminin stimulated myoblast proliferation and incorporation of [3H]thymidine in a dose-dependent manner. The stimulation is two- to threefold higher than on dishes coated with equivalent amounts of fibronectin and is observed both in the presence and in the absence of serum. These results suggest that laminin, a major component of the muscle basal lamina, may be actively involved in the development and regeneration of skeletal muscle.