The majority of chestnut orchards in Slovakia are damaged, to the different degree, by chestnut blight caused by Cryphonectria parasitica. Biological control of this disease by hypovirulent strains of C. parasitica has brought no due effect so far. Interspecific hybrids Castanea sativa × C. crenata represent certain hope for future in this respect. A goal of this work was to test resistance degree of the selected interspecific hybrids Castanea sativa × C. crenata and selected trees of C. sativa and C. crenata origin using stem sections and bark and wood sections as well as progenies from both open and controlled pollination of trees under study. Simultaneously the pathogenicity degree of the used fungal strains was also tested. The next objective of the work was to assess the effect of the selected environmental factors (climatic, topographic, edaphic characteristics) on the damage degree of chestnuts caused by chestnut blight on the selected localities of Slovakia. In tests on stem sections and bark and wood tissue sections susceptibility to the applied fungal strains was evaluated by the size of necrotic lesions formed around the inoculation place. In both tests necrosis size was more affected by inoculation date and fungal strain than by studied trees and in spring inoculations of these tests, necrosis size reflected better differences in the assessed resistance degree and in pathogenicity of used fungal strains (two virulent and one hypovirulent strain). In tests on two-year-seedlings of different progenies, pathogenicity of the applied strains was more clearly manifested in the summer months than in the spring or autumn. Differences in susceptibility among progenies after June inoculation in 2014 and May inoculation in 2016 were demonstrated by bigger differences in the size and growth rate of necrotic lesions. Hazard of seedling dying increased with increasing size and growth rate of canker wounds and with decreasing stem diameter of seedlings. Outcomes of resistance tests on seedlings suggest that higher resistance degree of two C. sativa C. crenata hybrids did not manifest clearly on the higher resistance of progenies derived of these hybrids. Effect of environmental factors on the occurrence and spread of chestnut blight was assessed on 11 localities. Totally 450 old chestnut trees was evaluated with regard to their damage caused by C. parasitica using six-stage scale from 0 (healthy tree) to 5 (dead tree). Following evaluation of damage degree of particular trees, index of health condition (Izs) was calculated for each locality. Chestnut blight occurred in 10 chestnut localities where Izs varied from 0.14 (Rovňany) to 4.47 (Krná, Gaštanská). Totally 350 trees were infested and damaged by chestnut blight in 2015 and 371 in 2016. None of the geographic and topographic factors under consideration significantly affected damage degree of the studied trees. Only a slight effect of slope aspect, solar radiation and distance of the tree from barrier was observed. The trees with the lower damage degree receive more solar radiation, grow more frequent on the slopes exposed to the south and closer to barriers (stands or groups of trees forming canopy). Analysed soil characteristics on the selected localities did not confirm differences in hydro-physical properties of soil between localities showing different degree of damage caused by chestnut blight. In majority of chestnut orchards chestnut blight occurred in the years with hot summer. The likelihood of disease occurrence in individual trees increases with increasing droughts, increasing stem diameter and distance of tree from barrier.