This article describes the data on isotopic effects of deuterium in various biological objects as the cells of methylotrophic, chemoheterotrophic, photoorganotrophic microorganisms, green algae as well as animal cells. It was demonstrated that the increased content of deuterium in water leads to physiological, morphological and cytology alterations of the cell, and also renders negative influence on cellular metabolism, while deuterium depleted water (DDW) with decreased deuterium content on 20–30 % exerts beneficial effects on organism. The maximum kinetic isotopic effect measured at ordinary temperatures in chemical reactions leading to rupture of bonds involving hydrogen and deuterium lies in the range kH/kD = 6–8 for C–H versus C–D, N–D...