A simple and selective method for the determination of amoxycillin in pure form and in pharmaceutical preparations is described. The procedure is based on the reaction of amoxycillin with 4-nitrophenol (I), 2,4-dinitrophenol (II), 3,5-dinitrobenzoic acid (III) or 3,5-dinitrosalicylic acid (IV) in alkaline medium. The method has been used for the determination of 1-24 mug/ml of amoxycillin trihydrate in solution. The method is selective for the determination of amoxycillin in the presence of its degradation products, other antibiotics and different amines that are normally encountered in dosage forms.