The total soluble nitrogen in sugar beet impairs sugar recovery during processing and is therefore called harmful nitrogen. It consists of amino N, betaine, nitrate and the non-identified residual N. For quality assessment in Germany, only amino N is determined as a representative of all soluble nitrogen compounds. The aim of the project was to study the effect of variety and environment on the components of harmful nitrogen and the relationship to each other. For the study beet brei samples from variety trials with 52 varieties at 22 sites in 2000 and 2001 were analysed. For total soluble N, amino N and betaine the effect of environment was higher than the effect of variety. Furthermore, interactions between environment and variety became evident. The data show a close correlation between the concentration of total soluble N and amino N, although the slope was not identical for all varieties. The proportion of amino N on total soluble N increased with increasing amino N concentration, irrespective of whether the amino N concentration was increased due to the influence of variety or environment. The proportion of betaine decreased with increasing proportion of amino N, since betaine showed not as much response to environmental factors as amino N. This clearly demonstrated that the proportion of these fractions on total soluble N varied and thus it cannot be judged as constant, neither among different varieties nor for one variety in different environments.