Objective: To assess how low-level laser irradiation affects T cells.Method: The case-control interventional study was conducted from November 2021 to April 2022 after approval bythe ethics review committee of the College of Medicine, Mustansiriyah University, Baghdad, Iraq, and comprisedhealthy individuals. Phlebotomy was used to collect 4ml of blood. A portion of each sample was exposed to 589nmlaser radiation, while the other portion was used as a control. The irradiated sample was divided into whole bloodand in-plate subgroups. Phytohemagglutinin was used for mitotic stimulation of T-lymphocytes, and cellproliferation assay was used to stimulate T lymphocytes measured using MTS assay (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium). Optical density was measured using enzyme-linkedimmunosorbent assay. Data was analysed using GraphPad prism software.Results: There were 35 subjects, 17(49%) males and 18 (51%) females, with an age range between 19-25 years, allwithout any disease or medication. Laser irradiation stimulated T-lymphocyte proliferation to levels that dependedon the dose of laser used. At energy 30J/cm2 there was a significant increase in the in-plate subgroup of irradiatedsamples compared to controls and between the two irradiated subgroups (p<0.05). At 50J/cm2 dose, there was asignificant increase in the whole blood subgroup compared to the controls (p<0.05). At 70J/cm2 dose, there was asignificant difference in the whole blood subgroup compared to the controls, and between the two irradiatedsubgroups (p<0.05).Conclusion: The stimulation of T lymphocyte proliferation by the application of a 589nm laser could have medicalapplications in the field of immune system enhancement.Key Words: Phytohemagglutinins, Phlebotomy, Lasers, Lymphocytes, Proliferation,Immunosorbent