6 normal females were found to have a level of folic-acid-binding protein (FABP) in their sera (mean level 345 pg/ml). Lysates of their various leucocytes were assayed and FABP found exclusively in the polymorph fraction. The sera and lysates were fractionated by Sephadex G-200 gel column chromatography and the molecular weight of the FABP appeared to be approximately 40,000. A hitherto unreported inhibitory effect of heparin on folate binding was noticed. Studies have been performed on folic-acid-binding protein (FABP) in various pathological states, but the levels found in normal people are usually considered too low to permit investigation. In an earlier study [3], 6 normal females were found to have levels in excess of 300 pg/ml whilst the mean level of 94 controls was 76 pg/ml. Sera and leucocyte lysates from these people have been used to estimate the molecular weight of FABP in normal people.