This work is devoted to further evaluation of pathological states in light-irradiated cells in terms of relationship between the level of reactive oxygen species (ROS) and polymorphonuclear neutrophil (PMN) count. Human leukocytes were isolated from 34 donors exhibiting flu-like symptoms, irradiated with a nonlaser blue light (2 and 5 mW cm(-2)) and examined for ROS production by a chemiluminescence (CL) assay. The level of ROS was measured as a basal chemiluminescence before (BCL0) and after (BCL) irradiation. In our preceding study (Sinyakov, M. et al. [2007] Photomed. Laser Surg.25, 257-263), PMN-oriented group analysis was applied to a data set divided into light-resistant and light-sensitive points, and cell responsiveness to light was suggested for prognostic evaluation of pathology. In the present work, BCL-oriented analysis was performed on the whole data set to evaluate the individual contribution of every point. BCL level and PMN count were confirmed to be independent variables. Sign-specific delta (DEL) values (DEL = BCL - BCL0) were assessed in relation to respective levels of BCL, BCL0 and PMN counts. DEL and BCL0 were found to be reliable photochemical indices of pathology. Taken together, the results obtained from group and individual analyses provide a novel outlook on the dynamics of pathological development and indicate a promising potential of the assay as a fast discriminator between the nonpathological state and different levels of pathology.