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Continuous-wave He-Ne laser exposures (Intensity=35 mW/cm2, lambda=632.8nm, Fluence range: 1J/cm2 to 50 J/cm2) on non-confluent and actively dividing human malignant glioblastoma cells was found to increase the cellular production levels of H2O2. Modulations in the cellular metabolic activity were detected (through the MTS assay) three days after laser irradiation. The metabolic activity was found to be dependent on the laser dose of exposure (i.e., fluence). In addition, three days after the laser exposure, the potential laser induced ldquobystanderrdquo effect was tested through the transfer of growth media from laser irradiated cells onto non-irradiated cells. After two additional days of incubation (5 days post exposure), the non-laser irradiated cells were found to have a significant increase in their metabolic activities. Modulations in the metabolic activities in the non-irradiated cells were found to be fluence dependent from the initial laser exposed cells treatment conditions. The results herein support the hypothesis of an important functional role for light enhanced cellular H2O2 generation to yield bio-modulatory effects locally and at a distance. The classical ldquobi-phasicrdquo modulation response of cells to light irradiation is hypothesized to depend upon the quantity of light-enhanced H2O2 molecules generated from the mitochondria and the number of cells which interact with the H2O2 molecules.