Extensive investigations on 11 patients with nemaline myopathy (six index patients, five relatives), their parents, and some healthy relatives were carried out. In one family, nemaline myopathy was inherited as an autosomal dominant trait. No linkage between the locus of nemaline myopathy and the locus of seven informative genetic markers (out of 25 investigated markers) was found. In two families an autosomal recessive inheritance could be demonstrated with certainty. In these families, both parents of each index patient had rods and an increased number of fibers with internal nuclei. In two other families, one or both parents of each index patient had an increased number of fibers with internal nuclei, also indicating the possibility of autosomal recessive inheritance in these cases. It can be concluded that there are two types of nemaline myopathy. However, these two diseases could not be separated on a clinical or histopathological basis.