A limited number of studies have been available to compare blood folate concentrations by the microbiological assay (MA) method with those using the chemiluminescent immunoassay (CLIA) method. We compared folate concentrations measured by Lactobacillus rhamnosus MA with those measured by CLIA (Access Immunoassay Systems) in human plasma/serum and erythrocytes pairs (n=35). The mean plasma folate by MA was significantly higher than that by CLIA (p<0.0001), whereas the mean erythrocyte folate by MA was significantly lower than that by the CLIA method (p<0.001). Plasma folate by MA significantly correlated with serum folate by CLIA (r=0.85, p<0.001). Similarly, the correlation between erythrocyte folate measured by MA and CLIA methods was significant (r=0.87, p<0.001). We conclude that folate concentrations obtained by CLIA are different from those obtained by MA, suggesting that it is undesirable for inter-laboratory comparisons when folate values are obtained by different methods. Although we evaluated only one CLIA method, we recommend careful evaluation of folate assay by each CLIA method before the use in clinical and research settings.