Abstract: ¹⁴C-Valine incorporaton experiment reflects the ability of protein synthesis during the course of T-lymphocyte transformation. Whole blood was incubated for 32 hours at 37℃,¹⁴C-Valine was added twenty-four hours before the cells were harvested, By employing the filter film method, the celis were harvest, they were counted by the liquid scintillation counter.26 LL and BL leprosy-vpatients,20 BT and TT leprosy patients and 26 normal. persons as controls were tested. The results show that the ¹⁴C-Valine incorporation radioactivity/0.2ml blood of leprosy patients, stands in normal range, But incorporation radioactivity/10⁵ lymphocytes of leprosy patients of two types decreased significantly(P<0.01)as compared with that of normal subjects, It reflects the impairment of cell-mediated immunity in leprosy patients. This experiment has the superiority of short incubation time,no need to use serum in culture medium and its preciseness.