The flow-cytometric read-out of the methemoglobin reduction test (G6PD flow-cytometric assay) detects functional G6PD enzyme inside the single red blood cell (RBC). We studied the correlation with the gold standard spectrophotometric assay in blood samples from Asian and Afro-American adult volunteers and the G6PD flow-cytometric assay showed to be superior in diagnosing G6PD levels in heterozygous women and subjects with anemia. By delivering a more precise quantification of the number of G6PD deficient RBCs as compared to the spectrophotometric assay, it might be more reliable in predicting drug induced hemolytic risk. We have also used the technique to study the capacity of Plasmodium vivax to infect G6PD mutated reticulocytes in-vitro and we have ongoing studies where we are using the assay to analyze dynamics of hemolysis in subjects treated with primaquine. In the future the G6PD flow-cytometric assay could be used to characterize the time-course of the enzymatic activity during maturation and senescence of RBCs with different G6PD mutations; to study infection dynamics with different Plasmodium species and to assess hemolytic response to different drugs or drug regimens. A simplified flow-cytometry based point-of-care device could be developed for assessment of G6PD status in the field which would be especially useful in regions with high prevalence of anemia and hemoglobinopathies.