The principles of phytomonitoring and its applications in phytophysiology are considered. The experimental installation (phytomonitor), designed for complex investigation of the state and functions of a vegetating plant, was constructed on the basis of a multichannel recording system. The phytomonitor provides for long-term continuous measurements of parameters (up to 20) that characterize the functional state of a plant and environmental conditions. One group of parameters was monitored from the shoot: transpiration, leaf turgor, water flow in the xylem, electric conductance of the stem, stem elongation rate, weight increase, pCO₂, temperature, and illuminance. Another set of parameters was monitored from the nutrient solution: pH, pK, pCa, pNH₄, pNO₃, pCl, pCO₂, electric conductance, redox potential, and temperature. Examplary experiments on phytomonitoring were performed with various plant species under steady-state and transient conditions. The potential applications of phytomonitoring are discussed in relation to the following topics: source-sink relationships in the root-shoot system, diurnal and subdiurnal oscillations of ion transport in the roots and transpiration in the shoots, the kinetics of induction and destruction of ion-transporting systems in the roots, interaction of ion and water flows in short-and long-distance transport, plant responses to stress factors, etc.