1. The chromosome numbers of 10 species of the genus Viola in the Netherlands were determined. 2. Viola riviniana has various chromosome numbers: 2n = 35, 40, 45, 46, 47 (most often 2n = 40). 3. It was not possible to find a correlation between the external morphology and the various chromosome numbers in V. riviniana. 4. Despite the variability of V. riviniana it proved impossible to divide the Dutch material into subspecies. 5. Some differential characters of V. riviniana and V. reichenbachiana are described. 6. V. canina is not variable in cytological respect in the Netherlands. 7. V. calaminaria is not related to V. lutea but to the V. tricolor complex.