The nitrogen accumulation in Italian ryegrass (Lolium multiflorum Lam.), perennial ryegrass (Lolium perenne L.), white mustard (Sinapis alba L.) and tansy phacelia (Phacelia tanacetifolia L.), under- or aftersown as nitrogen catch crops to spring barley (Hordeum vulgare L.) and field pea (Pisum sativum L.), was studied in three field experiments. The effect of catch crop incorporation in the soil on the yield and N accumulation in succeeding crops was also investigated. An aftersown catch crop should be used for pea, since undersown ryegrasses reduced the pea yield. Undersown perennial ryegrass or an aftersown catch crop can be used for spring barley. The catch crops had accumulated up to 70 kg N ha-1 at the time of ploughdown in early December. The nitrogen accumulation in catch crops following pea was significantly higher than in the catch crop following barley supplied with 100 kg N ha-1. Barley and pea straw incorporated in the soil reduced the N accumulation in the aftersown white mustard, but when distributed on the soil surface in perennial ryegrass plots, it had no influence on the N accumulation in the ryegrass catch crop. The amount of inorganic N in the ploughlayer in April was significantly reduced by incorporation of ryegrass in early December relative to plots without catch crops, and the yield of a succeeding barley crop was reduced. No consistent effect of white mustard incorporation was observed on the succeeding barley crop yield.