The fate of the carbon from photosynthetically assimilated 14CO2 and the nitrogen of rootapplied 15NO3 was studied by harvesting plants at intervals after a week's feeding period, either early (34–41 d after sowing) during vegetative growth, or late (112–19 d) as plants were fruiting. Only 23 per cent of the early fed 14C but more than 90 per cent of the early-fed 15N survived in plants until maturity (155 d). Efficiency of transfer of early-fed 14C to seeds was 2 per cent, that for early-fed 15N, 51 per cent. Assimilatory activity before flowering had little direct relevance to the carbon nutrition of seeds but provided approximately one-fifth of the seeds' requirement for nitrogen. Early or late-fed 15N was mobilized slowly for reproductive development, seeds at all 15 reproductive nodes deriving benefit, late-forming ones more so than those developing earlier. Vegetative organs on a young shoot lost previously acquired 15N at rates within the range 0.5–2.4 per cent per day. The released nitrogen was first taken up by the root and younger parts of the shoot, but much was later traced to the seeds. Late feeding of 14C or 15N resulted in a high (74–6 per cent) efficiency of transfer to seeds, most of this appearing to be donated by, or cycled through, vegetative parts of the reproductive zone of the shoot. The significance of past and current assimilation in fruit nutrition is discussed.