“…It is not affected by prior administration of antibiotics or of antifolate drugs and the red cell folate need not previously be deconjugated. Numerous assay kits are now available and their performance compared with microbiological assay has been evaluated in several recent publications (Kubasik, Votosin & Sine 1975, Waddel et al 1976, Hill & Dawson 1977, McGown et al 1978. Although radioassay measures all the circulating folate rather than specific analogues, it tends to yield lower results-ranging from 50% (Rothenberg da Costa & Rosenberg 1972) to 90% (Waddel et al 1976) of those obtained by radioassay and iodinated kits have been found to give consistently lower values than tritiated kits (Kubasik et al 1975).…”