Chestnut blight, caused by Cryphonectria parasitica Murr. Barr, is the most serious disease of chestnut trees in Turkey on which several studies related to biological control were conducted. The aim of this study was to determine the cause of the occurrence of healing cankers on untreated chestnut trees and the role of carriers in the spread of hypovirulence by laboratory tests, and to discover the effect of some environmental factors (temperature and relative humidity) on the natural spreading of hypovirulence. The study was carried out in a chestnut grove where biological control studies of the disease had been performed in previous years. Bark samples were collected from healed cankers and 388 possibly hypovirulent isolates were obtained. Two of them that were white converted virulent isolates to hypovirulent ones, but others developed yellowish cream-colored mycelia and did not convert virulent isolates. dsRNA analysis was performed on randomly selected possible hypovirulent isolates collected from healed cankers. After the virus concentration had increased, dsRNA-positive reactions were obtained for 56.73% of the isolates. Thirty-one possible hypovirulent isolates from Formicidae and Gastropoda did not convert virulent isolates to hypovirulent ones. dsRNA analysis was performed on these isolates and 61.29% of them containing dsRNA were observed in the invertebrates collected from cankers that had healed from hypovirulence. It was also observed that there was no significant difference among the date of average temperatures and date of relative humidity from 3 different altitudes. It was determined that the reason for the occurrence of the healed cankers on untreated trees was the natural dissemination of hypovirulence, ants and snails might have played a role in the natural dissemination of hypovirulence, and healed cankers mostly occurred on the western sides of shaded slopes.