On the basis of Finnish statutory variety trial data, the contribution of new varieties to cereal yields has been investigated. Such data have been collected since 1973. The data used contained the results of 2037 field trials testing 224 new barley cultivars, 163 new oat cultivars, 154 new spring wheat cultivars, 48 new winter wheat cultivars and 52 new winter rye cultivars. The data indicated a continuous increase in the annual yield of all the cereal species. The increase could be attributed in part to the genetic improvement of varieties and in part to changes in farming practices and environmental conditions. By using modern mixed model techniques it was possible to separate the effects due to genetic improvement from those due to the other factors. The main results show that in 1973–2003, new varieties contributed to an increase of 0·64, 0·41, 1·01, 0·63 and 0·97%, respectively, in the mean annual yield of barley, oats, spring wheat, winter wheat and winter rye. The research approach was based solely on existing data; new field experiments were not needed.