The response of Vicia sativa (cvv. Languedoc, Blanchefleur and Morava) and V. benghalensis (cv. Barloo) seed yield to seeding rate was examined in 9 field experiments across 2 years in south-western Australia. There were 2 types of field experiments: seeding rate (20, 40, 60, 100 and 140 kg/ha) x cultivar (Languedoc, Blanchefleur, and Morava or Barloo), and time of sowing (2 times of sowing of either Languedoc or Blanchefleur) x seeding rate (5, 7.5, 10, 15, 20, 30, 40, 50, 75 and 100 kg/ha).A target density of 40 plants/m(2) gave 'optimum' seed yield of vetch in south-western Australia. In high yielding situations, with a yield potential above 1.5 t/ha, the 'optimum' plant density for the early flowering cultivar Languedoc (85-97 days to 50% flowering) was increased to 60 plants/m(2). The later flowering cultivar Blanchefleur (95-106 days to 50% flowering) had an optimum plant density of 33 plants/m(2) at all sites, regardless of fitted maximum seed yield.Plant density in the range 31-38 plants/m(2) was found to be adequate for dry matter production at maturity of Languedoc and Blanchefleur. For the remaining cultivars Barloo and Morava we were unable to determine an average optimum density for either dry matter or seed yield due to insufficient and/or inconsistent data.