Abstract

Fluorimetry, paper and column chromatography, and bacterial inhibition assay have been compared in the quantitation of serum or blood phenylalanine at levels ranging from 1 to over 30 mg/100 ml. Special attention was paid to levels of 2 mg or less and to those in excess of 20 mg/100 ml, since these have therapeutic implications. Bacterial inhibition assay, under routine conditions, tended to read low or not at all at 2 mg or less, and to read high above 20 mg/100 ml so that it `failed safe' under such conditions. Paper chromatography was shown to be a simple, rapid, and economic method of getting accurate results at all levels in the range examined.