In organic farming, nitrogen is supplied to the nutrient cycle of farms primarily through biological nitrogen fixation. In Finland, the most common way of doing this is cropping of perennial red clover-timothy leys. The clover content is an important factor in organic grassland management in utilizing nitrogen from the atmosphere for the field and the farm. The aim of this study was to determine the variation of the yield level and clover content of one-, two- and three-year-old leys. This was done by taking ley samples from experimental plots and organic farms. The yields were highest in the two- and three-year-old leys and lowest in the one-year-old leys in the experimental plots in 1994–1996. The yields ranged from 5300 to 7500 kg ha~' dm (dry matter). The year also had a statistically significant effect on the ley yields; in one location having a greater effect on the yields than the age of the ley. On the farms, the yields decreased from two-year-old (6500 kg ha−1dm) to three-year-old (4900 kg ha−1dm) leys in 1998, with no significant change between one- and two-year-old leys. The clover content (20–80% of dm) and total nitrogen content (1.5–4% of dm) of the yields varied so much in the experimental plots that no clear conclusion could be drawn. In the farm samples the clover content diminished in the same order as the yields. On farms there may be problems in maintaining the clover content and yield level high enough for three years which is economically favourable.