Temporal and spatial aspects of the synthesis during embryogenesis and the mobilization after germination of the major seed storage proteins of rape were examined in a combined biochemical and immunocytochemical study. Monospecific polyclonal antibodies raised against napin and cruciferin were used to examine the distribution of the newly synthesized storage proteins. Both of the storage proteins were deposited as small inclusions inside large central vacuoles in the cells of developing rape cotyledons and were present in equal abundance on a molar basis in all types of protein body at all stages of seed development and germination. Mobilization of both napin and cruciferin began on the 2nd day after germination and was largely complete by the end of the 3rd day. The accumulation of the 2 rape storage proteins occurred at almost the same time, as did their mobilization. In contrast, the accumulation of storage lipids began several weeks before that of the storage protein, while storage lipid mobilization did not start until after that of the storage protein. It was suggested that there could be a common mechanism governing the regulation of the synthesis and mobilization of the 2 major rape storage proteins which was different from that which was involved in storage lipid synthesis and mobilization.