In European countries the following final/intermediate host assemblages of Echinococcus granulosus are known to occur: (a) dog/sheep; (b) dog/horse; (c) dog/cattle; (d) dog/pig, (e) dog/reindeer (= "northern form" of E. granulosus). The parasites involved in cycles a-d have been identified as distinct strains in various countries. Epidemiological aspects relevant to intraspecific variations and strain characteristics are described. In E. multilocularis there are some indications for intraspecific variability but it is yet unknown whether or not they are of epidemiological or other significance. There is clear evidence that E. multilocularis, the dog/sheep strain and the "northern form" of E. granulosus are infective for humans; the status of the other strains regarding infectivity to man is still unclear.