Abstract
Direct assay of serum folate by mixing serum with a mixture of L. casei and medium without autoclaving was found to provide serum folate results similar to those by extraction of serum with heat. This procedure was found more reliable than that using the same technique with chloramphenicol and a strain of L. casei adapted to grow in this material. A portion of apparent folate activity assayed in haemolysates by such direct assay was found to be due to material other than folate. It is recommended that heat extraction of haemolysates be continued for determination of whole blood folate, or that an additional standardization of technique be included if direct assay is used.