We have found that exposure of a small skin area (400 cm2) of healthy volunteers to visible (400 - 2000 nm) incoherent polarized (VIP) light (degree of polarization > 95%) in therapeutic doses (4.8 - 9.6 J/cm2) induces a rapid structural-functional modification of erythrocytes, leukocytes, and some plasma components in the whole circulating volume of blood. We have recorded changes in: lipid peroxidation (LPO) produce content in erythrocyte membranes, deformability and viscosity of erythrocytes, phagocytotic activity of monocytes, cytotoxic activity of natural killer cells against target malignant cells, release of bactericidal proteins by granulocytes, plasma content of LPO-produces and pro-inflammatory cytokines, interleukine-1 beta and tumor necrosis factor-alpha, total anti-oxidant activity of plasma. Most of these effects were of regulative character, as their direction and extent depended on the initial level of the studied parameters: the initially low indices increased, while the initially high ones decreased or remained unaffected. In 24 h the changes were still detectable in 33 - 62% of volunteers. We have shown a great similarity of the blood changes induced by the skin exposure and by the direct irradiation of blood in vitro. Moreover, we obtained an evidence that the light-induced rapid modification of the entire circulating blood resulted from the direct effect upon it of transcutaneously irradiated blood, rather than of other systems of organism. Since many pathological conditions are characterized by an increase in LPO processes, by disturbances in blood rheology, by decrease in natural resistance and immunity, correction of their parameters with the VIP light might be a key mechanism of its therapeutic efficacy.