The authors analyze the interaction of timolol maleate (Timoptol,Léčiva Prague) with free amino acids with regard to the effect on intraocular pressure.The different colour reaction of an amino acid mixture with Timoptol,the decline of radioactivity of Na [I 125 ]tyrosine with Timoptol and the formation of 8 radioactive fractions after addition of Timoptol to Na [I 125 ]indicate:a)the specificity of interaction of each amino acid with Timoptol;b)suggest that between Timoptol and free amino acids a firm covalent bond develops with the concurrent development of a new biologically active metabolite.Evidence of the presence of a new metabolite is important from the aspect of understanding and more accurate definition of the action of Timoptol in tissue structures of the eye and thus also for possible effective treatment of glaucoma.

        Key words: timolol in structures of the eye,amino acids and Timoptol,reaction of Timoptol with Na [I 125 ] tyrosine and Na [I 125 ]protein A