Methods for the assay of pantothenic acid in blood, urine, and cerebrospinal fluid using Lactobacillus plantarum and Tetrahymena pyriformis are presented. Tetrahymena, grown in a synthetic medium, provides a reliable assay control for establishing the range of the vitamin content in biologic fluids. The results show that pantothenic acid exists in the combined form and is equally concentrated in blood and cerebrospinal fluid; in urine it exists in the unconjugated form.