The preparation of two acidic metabolites of timolol, 2-[4-(4-morpholinyl)-1,2,5-thiadiazol-3-yloxy]acetic acid and d,l-3-[4-(4-morpholinyi)-1,2,5-thiadiazol-3-yloxy]lactic acid is reported using 3-chloro-4-(4-morpholinyl)-1,2,5-thiadiazol as starting material.