Folate is an essential vitamin involved in a number of biological processes. High affinity folate binding proteins (FBPs) exist both as glycosylphospha-tidylinositol-linked, membrane associated folate binding proteins and as soluble FBPs in plasma and some secretory fluids such as milk, saliva and semen. The function and significance of FBPs are unresolved, however, it has been suggested that they may facilitate folate uptake, . during suck-ling.