During myogenesis, muscle contractile protein gene expression is induced and the products are used to assemble the contractile apparatus characteristic of striated muscle. The different muscle proteins are accumulated in a fixed stoichiometric ratio related to their organization in the contractile apparatus. We have examined the relationship between contractile protein gene expression and the maintenance of stoichiometry at different stages of human myogenesis. Essentially all of the known components of adult human skeletal muscle thick and thin filaments have been cloned in the form of cDNAs and used to generate isoform-specific DNA probes. The expression of fast, slow, and cardiac isoforms was measured in human myogenic primary culture and in fetal and adult human skeletal muscle. We observed that neither fast nor slow nor cardiac isoforms are coordinately regulated at the level of comparative transcript accumulation throughout myogenesis. Thus, the stoichiometry of contractile protein levels cannot be explained by coordination of expression in each of these isoform classes. However, we find that the stoichiometry of mRNA accumulation of each gene family is very similar among three developmental stages: myotubes, fetal skeletal muscle, and adult skeletal muscle. This is consistent with the possibility that the maintenance of stoichiometry between the contractile proteins could be largely regulated by the total accumulation of mRNA from each of these gene families.