We have collected all the reported cases of Echinococcus cysts recovered in every surgical ward in Mashhad since their establishment. At the same time we searched corpses of livestock which had been slaughtered in Khorassan's slaughter houses in different days since 1969 for evidence of cysts, and also dogs, 2 wolves, 4 jackals and 11 foxes which had been killed with strychnine, for adult worms. Occurrence of hydatid cyst infestation was found in 478 reports of surgical operations amongst 43,196 cases operated for various diagnosis including hydatidosis. The number of hydatid cyst infestation amongst 15,691 corpses is as follows: 881 out of 12,311 sheep and goats, 378 out of 3380 cattle and camels. The dogs' infestation was rather high as we found adult Echinococcus worms in 50 out of the examined 266, which gives a percentage of 18.79. But no worms could be found in the 2 wolves, 4 jackals and 11 foxes which were examined. All the adult worms examined were Echinococcus granulosus.