Studies were initiated to investigate the potential for seedling disease of alfalfa under controlled conditions in a Kentucky soil naturally infested with Aphanomyces euteiches. Germinated seeds of 21 alfalfa cultivars or experimental lines were planted into pots containing a Heitt silty clay loam and placed in a growth chamber at 24 C for 3 wk. Pots were irrigated with either a 5-mu-g/ml metalaxyl solution (to control Pythium and Phytophthora spp.) or a solution of 5-mu-g/ml of metalaxyl + 10-mu-g/ml of hymexazol (to control A. euteiches also). In pots irrigated with metalaxyl alone, plants of cultivars susceptible to A. euteiches generally were killed or severely stunted. When A. euteiches was controlled with hymexazol, root rot was nearly eliminated, and dry weight and nodulation were greatly increased in all cultivars and experimental lines. The dry weight of seedlings treated with metalaxyl alone increased significantly with increasing resistance to A. euteiches. Given the disease potential observed in this study and the widespread distribution of the pathogen in the state, A. euteiches may be an important cause of seedling disease of alfalfa in Kentucky.