Intercropping of spring cereals in a permanent stand of white clover (Trifolium repens L.) is a novel, low input cropping system, and little is known about the agronomic management of this system. An experiment was conducted over two growing seasons in 1998 and 1999 to determine the impact of a white clover intercrop on spring oat (Avena sativa L.) growth and grain yield at three different seeding rates of oat, and also to determine the effect of the three different white clover cultivars (cv. Aran, cv. S184 and cv. Milo), on weed pressure and growth of the oat crop. The clover cultivars differed in stolon morphology and leaf size. Oat in monoculture was included for comparison. The white clover intercrops did not reduce the weed pressure compared with oat in monoculture. Oat grain nitrogen concentration and content was raised in the intercropped oats. Grain yields in an intercrop were similar to those in a monoculture. Oat seeding densities did not affect grain yields. The oat grain yields in 1998 were significantly higher with S184 as intercrop. In 1999 it was directly opposite, grain yields were significantly lower with S184 as intercrop.