The Drosophila single-minded gene is expressed in the embryonic central nervous system midline cells and plays a critical role in central nervous system development. Additional expression of single-minded is found in a subset of ventral muscle precursor cells. Null mutations of single-minded result in an alteration of the ventral oblique muscles, such that muscle fibers form inside the embryo above the central nervous system. This defect is due to the mislocalization of a subset of mesodermal precursor cells. The muscle defect observed in single-minded null mutations is not due to the absence of single-minded expression in muscle precursor cells and likely results from an influence of the central nervous system on ventral muscle development.