Relative pollen composition during the monthly sedimentation of river seston at different points in the reservoirs of some hydroelectric stations in Finland has been studied. Samples were taken in 8 reservoirs in the water courses of Kemijoki, Oulujoki, Kokemäenjoki, Paimionjoki, Pielisjoki and the Höytiäinen channel in 1974. The relative pollen composition reflects generally the present vegetation and the forest composition of the drainage areas of the rivers investigated. Particularly Pinus, Betula and Picea seem to be little effected by the time of sedimentation. Knowledge of the pollenflora in the Finnish river material is for its part significant for the evaluation of the pollen composition of the surface samples of the Baltic sediments