Eleven populations of the Heterodera avenae complex (four Spanish, two British, two French, and three Swedish) were studied by random amplified polymorphic DNA analysis. From 5 to 11 fragments were obtained with each of 14 random primers, with fragment size ranging from 200 to 2200 bp. Cluster analysis of the 11 populations, using 108 scorable markers, separate these populations into two main groups. These groups coincide with what is known as the "true" H. avenae and the "Gotland strain" or "British pathotype 3" of H. avenae. The results also clarify the relationships among some members of the H. avenae complex established previously using morphological and biochemical criteria. Key words : cereal cyst nematode, CCN, Heterodera avenae, RAPD.