Globin chain synthesis and globin mRNA content were studied in blood cells of a patient homozygous for Hb Lepore. Peripheral blood cells incubated with tritiated leucine synthesized approximately 1.5 to 3% as many Lepore globin chains asαchains. Globin mRNA in peripheral blood cell RNA was assayed by molecular hybridization assays using humanαandβcDNA, and the results indicated the presence of approximately 1% to 2% as muchβ-like mRNA (presumablyδβLepore mRNA) asαmRNA. The amount of Leporeδβchain mRNA in peripheral blood cells is therefore proportional to the amount of Lepore globin chain synthesis in the same cells. An incidental observation was the finding that peripheral blood cell RNA of this patient, at a time when she was being heavily transfused, contained substantially higher levels ofβ-like mRNA (relative to a mRNA) than in subsequent studies. Cell-free translation of this mRNA however revealed that it contained authenticβchain mRNA which must have been derived in some way from the transfused blood cells.