Physiological activity was estimated by such parameters of Chlorella's metabolism, as net primary production, respiration and primary production. Physiological influence of Humic Acids (HA) of different origin upon microalgae Chlorella vulgaris co. 157 has been investigated. HA preparations from different soils, preparation of fulvic acid from soddy-podzolic soil and industrial humic preparation “Gumat-80” of manufacture of Irkutsk firm "GUMAT Ltd" (extract from brown coal) were tested. Besides, profiles allocation of HA physiology activity was investigated for the chernozem and soddy-podzolic soils. Layers samples (every 6 cm), from the surface to a depth of 30 cm, were taken from this soils. Also, concentration of free radicals was defined in all HA preparations. The experiments showed, that all preparation using in this work pronounced physiological effect on the Chlorella vulgaris. Two peaks of physiological activity were observed in all experiments. But HA concentrations corresponding to the peaks were different for HA preparations from soddy-podzolic and from chernozem. This phenomenon was revealed by us earlier on corn coleoptiles (Chukov, Talashckina, 1996). The estimation of free radicals concentration in these HA preparations shows, that they obviously have the different mechanism of display of HA physiological activity. Relationships between parameters of Chlorella vulgaris metabolism and concentrations of HA preparations were different. In some cases HA preparations stimulated primary production, but in other cases, respirations. Preparations of chernozem's HA and "Humat-80" very strongly differ. Chernozem's HA (with 0-6 centimeters) very strongly stimulate respirations, but almost do not stimulate primary production. The industrial preparation "Humat-80" on the contrary stimulates primary production, but not respirations. In some experiments primary production remained on level of control, but the net primary production and respiration changed significantly with increase of HA concentration. HA from soddy-podzolic soil had approximately equally stimulated both respiration and primary production of Chlorella vulgaris, however had the most weak effect among preparations of soil HA. Industrial humic preparation “Gumat-80” had the best physiology effect. Experiments also showed that HA of buried soddy-podzolic soils, character of physiological activity approached to chernozem type. The lowest effect of stimulation was observed for the preparation of fulvic acid. Experimental data showed, that is very complicated dependence of various aspects of Chlorella vulgaris metabolism from humic preparations concentrations. Some mechanisms of physiological activity of humic preparations probably take place. Investigation of HA preparations extracted from layers samples showed, that physiological activity of humic substances varied in the profile of the soil, and in different manner for two studied soils. In soddy-podzolic soil profiles allocations of HA physiology activity were connected with the long history of this old-plowed soil and demonstrated the recovery of the humus activity in the soil. In the case of the chernozem, physiology activity was the smallest in first layer (0-6 cm), and the highest in the second layer (6-12 cm). After depth of 12 cm physiology activity just as concentration of free radicals regularly decrease. HA physiological influence on the processes of metabolism of microalgae had stable correlation with concentration of free radicals in the HA. When concentration of HA in solution was low, concentration of free radicals was correlated with the respiration, but when HA concentration was high, concentration of free radicals was correlated with the photosynthesis and the increase of biomass. It also can be explained by different mechanisms of influence of concentration of free radicals in HA on the metabolism of microalgae. Information received in this work can be used in furthers investigations on the mechanisms of the influence of free radicals concentration in HA on the metabolism of plant cells, and also in the investigations directed on the profiles allocation of physiology activity of humic substances. Methodology used in this study is convenient for the estimation of physiological activity of humic substances. It can be also use for express testing of humic industrial preparation, because this method is relatively simple. Research was supported by the grants of RFBR (04-04-49000) and MinPromNauki ( NSH ¹ 1634 2003. 4)