A simple assay is described for phospholipase A in chromatographic fractions. 0.01 ml of the fraction is added to 1 ml of a 1% solution of purified lecithin in ether (100 vol) — picoline (10 vol) — 4.5 mmol CaCl
2 (1 vol). The presence of phospholipase A is indicated by the appearance of a turbidity due to precipitation of lysolecithin. The lag period until precipitation occurs gives an indication of the relative concentration of enzyme present.