An integrated ultrastructural and immunochemical study of storage protein synthesis was followed on early stages of developing peanut embryos. Whereas it was reported that storage proteins are not present in very immature embryos, e.g. prior to the formation of storage vacuoles or during cytokinesis, we detected α-arachin (the major storage protein) in the smallest embryos feasible to collect—embryos 0.5 to 1 mm long. These embryos contained meristematic cells 10 to 20 μ in diameter which showed the normal complement of organelles; however, no storage vacuoles were observed in these cells. Heavy synthesis of α-arachin coincided with the microscopic observation of protein granules in storage vacuoles of cells in embryos that were about 10 mm long.