In the world-wide literature the role of predators and food shortage are considered as responsible for mortality of eggs and nestlings. In synantropic altricial hole-nestling birds such as sparrowsPasser domesticus (L.) andPasser montanus (L.) the predation plays unimportant role and in spite of this, mortality of eggs and nestlings can exceeded 50%. The role of microorganisms, heavy metals, pesticides and food shortage were investigated as possible causes of embryo and nestling deaths. About 70% of eggs that not hatched were infested with such pathogens asEscherichia coil, Staphylococcus epidermitis and several, more rarely occurring others. Considerable percentage of nestlings died due to pathogenic impact of such factors asEscherichia coli, Isospora lacazei, Candida spp., heavy metals and pesticides. As one effect of such interaction, the level of sublethal doses of heavy metals and pesticides are much lower that reported in the literature.