Laminin is reportedly an extremely potent neurite-promoting agent in vitro. We investigated the effect of laminin on regeneration of axons in vivo, using a cord of polyester filaments coated with laminin as a guide, replacing a 10-mm segment of the rat sciatic nerve. After 4 weeks the cross section of the nerve guide at its midportion was examined under an electron microscope. Many regenerated axons were seen in the laminin-coated group, whereas no axon was observed in the controls. We conclude that laminin guides the regeneration of axons in vivo.