Seeds of Vicia faba (L) become fully mature in about 130 days from the fertilization of the ovule. After an initial phase of cell division, storage protein is synthesised in the cotyledons. During the stage of storage protein synthesis, rRNA synthesis occurs concomitant with synthesis of ER, suggesting that storage protein synthesis is mediated on membrane bound ribosomes by mRNA(s). Analysis of the nucleic acids during cotyledon development did not lead to the identification of any non-ribosomal RM species. A fourth rRNA was identified, which had a molecular weight of 52,000 daltons and was hydrogen bonded to the 25S rRNA species. Attempts to identify rRMA precursor molecules in cotyledons and roots were unsuccessful, though in the latter the bacterial precursor molecule to the 163 rRNA was identified. Isolated polyribosomes, from cotyledons at various stages of development, had similar profiles and their constituent nucleic acids were degraded, indicating that they were cleavage products of larger in vivo units. The rRNA cleavage products arising during polyribosome isolation were characterised by their molecular weights. The properties of diethylpyrocarbonate as a nuclease inhibitor were reinvestigated and it was found to be incapable of effectively inhibiting high concentrations of nucleases. The extraction of polyribosomes in the presence of diethylpyrocarbonate effectively protected the polyribosome against HNase during the later stages of the extraction procedure, but not during the initial stages resulting in marked rRNA cleavage and the formation of ribosomal subunits. The use of antllegumin as a method in the identification of a mRNA is discussed.