Backgroundcontributes substantially to patient morbidity and mortality.In this study we investigatedthe range and distribution of T-lymphocyte.Subsets CD3helper/inducer cell,.th ),CD8: Severe immunosuppression occurs after large thermal burn and probably+ (T cells) CD4+ (T+ (T suppressor /Cytotoxic cells ,TS/C), CD3+CD4thermal injury.+/CD3+CD8+ ratio,CD19+ (B cells) and CD16+ (NK cells ) in patiens followingMethodsstudied.The total body surface area of the burn injury, ranged from 30 to >70%.Wholeblood samples were collected at three and seven days postburn. Partec flowcytometrysystem and triple color flowcytometry reagents (Dako Co), were used to evaluate peripheralblood lymphocytes population of patients admitted at the Motahary Burn Centerin Tehran.:Forty male, aging 18-60 years with major thermal injury wereResultsreduction in relative number of CD3postburn.CD4range in seven days following injury.CD19burn patients at both three and seven days. The number of CD16declined in three days and moderately increased on day seven,following injury.Thus, the data showed that thermal burn injury suppressed T-lymphocyte subsets proliferationin various days .In addition, all compartments of showed phenotypic changesin the 3th and seventh days after burn, in different groups of age.Thermal burn injurysuppressed T cell subsets proliferation on day 3 and 7 postburn, when compared to normalcontrols.(P <0.05) at 3 and 7 days post burn.: Compare to healthy controls, patients with burns have shown a significant+, CD4+ and CD8+ T cells at three and seven adys+/CD8+ ratio were below normal range in three days and remained in normal+ B cell populations were elevated in+ NK cells were significantlyConclusion factor in immunosuppression and development of sepsis in thermal burn patients.Significant changes in lymphocytes population could be an important