We have developed the digital holographic interference microscope (DHIM) for real time three -dimensional (3-D) imaging and quantitative study of phase microscopic objects (MOs). The instrument integrates holographic interference microscope with digital processing of interferograms. The experimental procedure, allowing calculating microscopic objects thickness and 3-D imaging from the measured phase shift, is presented. The method has been applied to study 3-D morphology of red blood cells in norm, in pathology and under influence of physical and chemical factors in vivo. It has been found that morphologic changes of erythrocyte population had nonspecific character. Our investigations have proved that erythrocytes 3-D morphology reflects the state of a living organism and the level of its biological response on different external factors influence.