Wild emmer from 73 collection sites, including 107 accessions from Israel, two from Lebanon and one from Turkey, were evaluated for resistance to powdery mildew in field nurseries in Israel and the Netherlands. The wild emmer entries displayed a diversity of responses to powdery mildew infection, ranging from high resistance to complete susceptibility. Most entries were resistant in at least one of the nurseries; several entries proved to be resistant in all the tests. Comparing the reactions of 47 wild emmer accessions tested in six nurseries, 11 markedly different patterns were discerned, indicating the probable presence of several different resistance genes. Genes for resistance to powdery mildew appear to be very common in wild emmer indigenous to Israel. Resistance was found in accessions from most collection sites, in all the geographic regions represented in the collection. The common occurrence of resistance and the apparent diversity of genotypes makes wild emmer a rich gene-pool for resistance to powdery mildew. Since genes for resistance to wheat pathogens can be quite readily transferred to cultivated wheat, wild emmer may be utilized as a valuable source of powdery mildew resistance in wheat breeding.