[The action of chemical agents at ultralow doses on biological objects].

The published data on the effect of low and ultralow (up to 10(-17] doses of chemical agents on different biological systems have been reviewed. A concept of action of ultralow doses has been proposed on the basis of a notion of complex hierarchical structure of regulation in biological systems where response to strong and weak actions is carried out by different mechanisms and pathways. The times of transport of molecules of biologically active compounds to targets have been calculated on the basis of the principle of the first boundary approach by Brown's particle. Probabilistic models of mechanisms leading to complex dose dependency have been analyzed.