Abstract: A △P₂ method is presented for the determination of the degradation product,p-aminobenzoic acid, in procaine-HCl injections. With phosphate buffers of, pH 2.90 and pH 7.50 as solvents, the △P₂ coefficient calculated over the wavelength range 228.6～288.6 nm at 12 nm intervals using 6 point quadratic orthogonal polynomial is independent of procaine-HCl. Mean percent recovery for 9 separate determinations was 100.4±2.4. This method is simple and the results obtained are reliable. The proposed method can also be used to detect the limit amount of PABA in procaine-HCl injections.