In the above-ground part of 12 different spring barley genotypes the phenomena were studied as follows: nitrate reductase (NR) activity, nitrate nitrogen (nN)-, ammonium nitrogen (aN)-, total nitrogen (tN)-, and soluble sugars (sS)-concentration, physiological yielding characteristics, their variability and relations during vegetation (field experiments). Significant genotypical differences in NR activity were not ascertained until in the shooting and especially in anthesis and milk ripeness. Of the parameters observed nN- and tN-concentration showed the greatest and the smallest genotypical differences during vegetation, respectively. Variability of the seasonal mean values was as follows [%]: NR activity -12.9; nN-conc. -43.7; aN-conc.-14.3; tN-conc. -7.9; sS-conc. -15.6 and dry weight of 1 plant -19.7. NR activity was in a positive correlation with nN- and tN-concentration and in a negative one with sS-eoncentration except for the period of anthesis. Similar negative correlations were noted between concentrations of sS and nN and between those of sS and tN. A positive and most significant relation was found also between N-translocation from vegetative matter to corn, N-harvest index, grain harvest index, further between grain yield, N-harvest index and grain harvest index. The results are discussed with regard to development of genotypical differences in these parameters and to possibilities of their use as selection characteristics.