Developing grains were harvested from wheat plants grown in pots which had received additional late P-fertilizer applications. By sequential extraction of milled grain samples of different developmental stages total P (P tot ) and the P-fractions lipid-P (P lip ), phytin-P (P phy ), inorganic and soluble ester-P (P i+e ) and residual-P (P res ) were determined.-Due to the late P-application, grain yield, P tot , and P phy content of ripe grains were increased by 14%, 58%, and 80% respectively, compared to the control. 93 % of the P which accumulated additionally in the grains as a result of the late P-application, were found to be P phy .-During grain development the amounts of P tot and P phy per 1000 kernels increased steeply whereas those of P lip and P res were not significantly affected by the stage of grain development or by the rate of P-application. P i+e increased during the first stages of grain development but subsequently decreased towards nearly the same low level regardless of the treatment.-The increased phytin concentration in the ripe grains resulted in a decreased zinc bioavailability as was indicated by feeding experiments with growing male rats.