In Sweden Erlandsson (1942) showed that the species Parnassia palustris L. has two chromosome numbers, 2n = 18 and 2n = 36. Rozanova (1940) found the same numbers in plants collected in the U.S.S.R. Some morphological differences could be demonstrated in the Swedish material (Erlandsson, 1942). This was confirmed by Löve and Löve (1944) and, therefore, these authors (1950) distinguish 2 species: the diploid Parnassia palustris L. em. Löve and the tetraploid Parnassia obtusiflora Rupr. em. Löve, also separated by sterility barriers and by their geographical distribution. In the Netherlands a tetraploid population was found by Gadella and Kliphuis (1963). As the tetraploid population occurs in an area situated far south of the circumpolar distribution area of the tetraploid plants, it seemed worthwhile to determine the chromosome numbers of other plants of Parnassia palustris L. growing in the Netherlands.