Zein mRNA was isolated from membrane-bound polyribosomes of developing maize kernels by oligo(dT)-cellulose chromatography. Translation of the mRNA in vitro yielded protein similar to native zein in amino acid content, ethanol solubility, and mobility on sodium dodecyl sulfate-polyacrylamide gels. The zein mRNA sedimented as a homogeneous peak on sucrose gradients and contained a poly(A)-rich region based upon hybridization to [3H]poly(U). The mRNA had an apparent MW of 540,000 on agarose-acrylamide gels. It synthesized both 21,800 and 19,000 MW zein components in the wheat-germ cell-free protein synthesis system. The possibility of a polycistronic mRNA or 2 mRNAs of similar molecular weight is considered.