Ovicidal activity was studied in microscopic fungi penetrating into and destroying eggs of geohelminths surviving in the soil. The character of penetration was compared in eggs obtained mechanically with those obtained by means of a chemical process. A total of 13 strains of ovicidal fungi of 4 species were studied. The shells of eggs obtained by the chemical process were so altered that under the same conditions they were attacked and penetrated by the fungi much more than the eggs obtained by a mechanical way. The advantages and disadvantages of these two methods of eggs isolation are discussed.