The success of annual medic pastures in ley farming systems is largely due to their ability to establish and maintain a viable seed bank from which these pastures can annually regener-ate. A medic pod burial study was conducted to evaluate seed bank persistence of a range of commercially available and experimental annual medic lines under field conditions in southeastern Wyoming. The Medicago rigidula (L.) All. (tifton burclover) cultivar Laramie had the highest proportion of hard seed throughout the study period (1997-2001). After 5 yr of pod burial, this cultivar retained 56% of the origi-nal seed bank as hard seed within 5 cm of the soil profile depth. In contrast, the best of the Australian-developed cultivars Santiago (burr medic [Medicago polymorpha L.]) maintained 48% hard seeds within 5 cm soil depth after 3 yr of pod burial. The remaining Australia devel-oped cultivars maintained at least half the seed bank for just 1 yr at either the surface or 5 cm depth. our results demonstrated that Laramie annual medic has the ability to produce a large and viable seed bank capable of persisting for an extended period in southeastern Wyoming ley farming systems. © Crop Science Society of America.