The newest approach in the saturation fluorimetry of photosynthetic organisms by the
example of phytoplankton was developed. The theoretical model and the inverse problem of the
saturation fluorimetry are discussed. The results of evaluation of molecular photophysical
parameters of alga Chlorella pyrenoidosa under various stress factors, such as presence of DCMU
and Cu2+ ions are presented. The correlation between theese parameters and the parameters obtained
using Fluorescence Induction and Relaxation technique is discussed.