An automated system is described for the microbiological assay of serum and red cell folate concentrations using a chloramphenicol-resistant strain ofL. casei. Both serum and whole-blood haemolysates are assayed directly without previous deproteinization. Results by this method are comparable to those obtained by standard manual folate assays. Reproducibility within and between assays is excellent. Special advantages of the method are its simplicity of operation, economy of reagents, and capacity for dealing with large numbers of specimens (80-100 per hour). The latter makes it especially suitable for providing a regional diagnostic service and for population surveys of nutrition.

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