Deficiency of laminin α2 is the cause of one of the most severe muscular dystrophies in humans and other species. It is not yet clear how particular mutations in the laminin α2 chain gene affect protein expression, and how abnormal levels or structure of the protein affect disease. Animal models may be valuable for such genotype-phenotype analysis and for determining mechanism of disease as well as function of laminin. Here, we have analyzed protein expression in three lines of mice with mutations in the laminin α2 chain gene and in two lines of transgenic mice overexpressing the human laminin α2 chain gene in skeletal muscle. The dy^3K/dy^3K experimental mutant mice are completely deficient in laminin α2; the dy/dy spontaneous mutant mice have small amounts of apparently normal laminin; and the dy^W/dy^W mice express even smaller amounts of a truncated laminin α2, lacking domain VI. Interestingly, all mutants lack laminin α2 in peripheral nerve. We have demonstrated previously, that overexpression of the human laminin α2 in skeletal muscle in dy^2J/dy^2J and dy^W/dy^W mice under the control of a striated muscle-specific creatine kinase promoter substantially prevented the muscular dystrophy in these mice. However, dy^W/dy^W mice, expressing the human laminin α2 under the control of the striated muscle-specific portion of the desmin promoter, still developed muscular dystrophy. This failure to rescue is apparently because of insufficient production of laminin α2. This study provides additional evidence that the amount of laminin α2 is most critical for the prevention of muscular dystrophy. These data may thus be of significance for attempts to treat congenital muscular dystrophy in human patients.