Echinococcus granulosus is widely distributed throughout Iran, where a variety of animals act as intermediate hosts. In this study, the development and morphological characteristics of E. granulosus of sheep, cattle and camel origin were compared and, overall, the characteristics of larval and adult isolates from sheep and cattle, although similar, showed significant differences from those of the camel isolates, especially with respect to the size of rostellar hooks. Differences in the fertility rates of hydatid cyst in sheep, cattle and camel were recorded as 88%, 19% and 70% respectively. In dogs experimentally infected with the three 'strains' of E. granulosus, the rate of development was more rapid in the camel than in the sheep and cattle 'strain'. In addition, adult E. granulosus derived from the camel demonstrate differences in worm length, segmentation and size, shape, number and arrangement of the genitalia when compared with worms derived from sheep and cattle. The epidemiological significance of these findings is discussed in relation to human hydatid infections in Iran.