Terrestrial plants are able to accumulate arsenic to a substantial extent but survive the stress to differing degrees of vitality. The influence of arsenic on important energy and metabolic cycles does not yet have sufficient explanation. Parallel to the uptake and processing of arsenic species such as As(III) and As(V) by Silene vulgaris, the nitrogen uptake using a ¹⁵N tracer method was investigated. The results showed that the nitrogen uptake decreases with increasing arsenate concentrations applied to the plants. The reaction of the plants treated with arsenite changed from a depression at low arsenite concentrations to a strong increase with the largest quantity applied, exceeding the ¹⁵N-incorporation of the control plants. This behaviour underlines the divergent behaviour of the N-metabolism caused by both arsenic species. As(III) can be detoxified by complexation with peptides rich in SH-groups. As(V) acts as a phosphate analogue and interrupts diverse phosphorylation reactions.