Seed phosphorus (P) reserves are essential for seedling development; however, we hypothesise that the quantity of P in seeds will lose importance in cultivars that rapidly acquire it via their roots. Our objective in this study was therefore to investigate the onset of seedling P uptake in rice (Oryza sativa). This was addressed through 33P-labelled supply and through measuring P depletion in combination with the detection of P transporter activity in the root tissue of three rice cultivars during early development. 33P supplied to roots 4 d after germination (DAG) was detected in shoots 2 d later, indicating that P was taken up and translocated to shoots during early seedling development. Measurements of P depletion from the growth medium indicated that uptake occurred even at 2 DAG when roots were only 3 cm long. By day 3, P depletion was rapid and P transporter activity was detected in roots, regardless of the levels of seed P reserves present. We conclude that P uptake commences at the earliest stages of seedling development in rice, that the amount taken up will be limited by root size, and that genotypes with more rapid root development should more rapidly complement seed-P reserves by root uptake.