Foliar application of N fertilizer is an efficient strategy with respect to boosting grain protein content and matching plant N demand with the actual climatic conditions in the growing season. However, foliar N application implies the risk of leaf damage. We would like to develop wheat genotypes that are better suited for foliar N fertilization. Therefore, wheat plants were subjected to different fertilization regimes including foliar application of N to investigate the effect on plant growth and molecular-physiological parameters related to nitrogen use efficiency. Using 15N as a tracer, we have observed that an unexpected large proportion (about 50%) of the N applied to the leaves remained in the vegetative plant parts at maturity, suggesting a bottleneck in the translocation of N to the grain. As cytosolic glutamine synthetase is a central enzyme in the assimilation and translocation of N from the leaves to the grain, we analysed GS activity and protein levels. GS activity in flag leaf increased in response to foliar application of N although the levels of GS protein were similar for the different treatments and growth stages during grain filling. Currently, GS gene expression is under investigation using Q-PCR.