Human seminal plasma is extraordinarily rich in acid phosphatase which is mainly of prostatic origin. Based on the fact that the prostatic acid phosphatase is specifically and almost completely inhibited by L(+) tartrate, a comparatively simple and specific method for identification of stains of human semen (normal or aspermic) in the forensic laboratory has been developed. 0.5ml of a dilute stain extract is incubated in each of two test tubes both containing phenyl phosphate dissolved in citrate buffer (pH 4.9) but one having in addition, 0.04M L(+) tartrate. The phenol liberated by hydrolysis is visualised by the Folin-Ciocalteu method. A marked blue colour in the tube lacking tartrate and lack of colour in the tube with tartrate (with reference to control) indicate the stain extract to be of human semen. No interference has been noted from biological contaminants. A preliminary report was presented at the Winter School on Forensic Science, Nangal, India (Sivaram and Bami, 1969).