Lupins and cowpeas were fed at 0.0, 0.5, 1.0, and 2.0% liveweight (LW) to groups of 6 or 7 South Australian Merino rams for 11 weeks as supplements to a maintenance diet of grass hay. Productive and reproductive parameters were examined. Supplementation at all levels of either grain increased (P<0.001) LW, condition score, backfat thickness, and wool growth, with rams showing similar responses when given cowpeas and lupins. The weights of the pancreas of rams decreased (P<0.01) as the levels of supplementation increased. Semen characteristics (volume, concentration, motility, etc.) and response to freezing did not differ between the diets. Feeding either legume increased (P<0.001) testicular size, lupins giving a slightly greater response than cowpeas. Sperm production per g testicular tissue was not significantly altered. Increasing levels of either supplement increased (P<0.001) the weights of the seminal vesicles, more (P<0.01) so with lupins. The same effects occurred with the weight of epididymides except for rams fed cowpeas at the highest level. Histologically, the testes revealed an increase (F<0.001) in the number of round spermatogenic cell nuclei and the cross-sectional diameter of stage 8 tubules in rams after legume grain supplementation at 2.0% LW compared with controls. The response was higher in lupin-fed rams (P<0.05). Plasma luteinising hormone (LH) and follicle stimulating hormone (FSH) were measured in rams fed at maintenance or with lupins or cowpeas at 2.0% LW. Rams responded equally to all legumes. Concentrations of LH in peripheral blood increased (P<0.001) by 140% and FSH concentrations were elevated (P<0.01) 4-fold. Cowpeas, a tropical grain legume similar in nutrient composition to lupins, have similar potential when used as a supplement to improve productive and reproductive capabilities of Merino rams.