Ascochyta lentis was isolated from necrotic lesions on lentil seed purchased in commercial markets throughout Bolivia in 2000. Incidence of seed infection ranged from 1% to 34% and the fungi isolated were able to reinfect lentil foliage in artificial inoculations. Disease spread from seed to seedling in the field was confirmed by planting infected seed in a field previously free of the disease and observing Ascochyta blight on the foliage. In addition, disease spread between plants initiated from infected seedlots to those initiated from clean seedlots and from infected plants back to seed was also detected. These observations indicate that A. lentis infection of lentil seed is common in Bolivia and may represent an important inoculum source for Ascochyta blight epidemics in commercial lentil plantings.