Abstract : Septoria tritici blotch is among the most damaging diseases of wheat in the north of Europe. It causes important yield and quality losses. The objectives of this work are to better understand the behaviour of N metabolism and fluxes in the plant when varying N availability by leaves manipulation, fungus impact on plant senescence, while separating local effect around the disease symptoms and remote effect at leaf apex and in healthy organs, and finally the behaviour of N metabolism and fluxes in the plant and in the diseased leaves in the case of natural epidemics. Reducing N availability immediately leads to a reduced rate of N filling without any compensation by the other organs; while increasing N availability does not modify the rate of grain N filling because of a temporary storage in stems or sheaths. The green leaf area loss results from: i) septoria symptoms, ii) local senescence developing around disease necrosis, and iii) apical senescence which is highly correlated to N remobilization in healthy plants. Various contrasted septoria kinetics were evaluated for their ability to modify apical senescence. Results strongly suggest that apical senescence is either not or hardly affected by septoria. The effects of the disease on different biochemical markers of N metabolism and on grain N filling were studied on crops grown under contrasted management strategies referring to previous results. Nitrogen kinetics of non infected organs was never modified by the leaf disease. In diseased leaves, N assimilation metabolism prematurely switched to a remobilisation metabolism.