Abstract A rapid disc assay method has been standardized for determination of folic acid content of several dairy products. The method involves measurement of the zone of growth stimulation of Streptococcus faecalis around a disc containing folic acid extract on a deficient agar medium. The diameter of the zone of growth bears a logarithmic relationship to the concentration of the vitamin. The disc assay method takes 8 to 10 hr compared to 22 to 24 hr required for the turbidimetric method. The method appears to be fairly accurate, giving 90 to 95% recovery. The average folic acid contents of milk and Cottage, Cheddar, Blue, and Swiss cheese, as determined by this method, were 3.5, 44, 15, 40, and 6 μg/100g, respectively. These values agree with those obtained by the turbidimetric method. The method is also applicable to several fruits and vegetables.