It is well known that at final harvest the crown of sugar beet contains less sugar and more molassigenic compounds than the storage root. Only little, however, is known on the ontogenetic changes especially of the components of 'Harmful Nitrogen'. They were studied with two genotypes which differed in the a-amino-N content by a factor of almost 2; the plants were grown in field trials with 4 replicates in the year 2002 at three sites in Germany. Our results indicate that, independent of the genotype, both storage root and crown are a sink for sucrose whereas only the crown is a sink for 'Harmful Nitrogen'. The latter increased in the crown but declined in the storage root with increasing plant age. At any time point the concentration of 'Harmful Nitrogen' was severalfold higher in the crown than in the storage root. As a consequence, the low processing quality of the crown became even worse with increasing plant age whereas the opposite held true for the storage root. Genotypic differences stayed rather constant in the storage root but increased slightly in the crown with increasing plant age.