New terbium complexes of 2-oxo-4-hydroxy-quinoline-3-carboxylic acid derivatives are reported for determination of alkaline phosphatase (aPase) and codeine phosphate (CP). Complexation with terbium occurs by way of the oxygen atoms of the 4-hydroxyl group and the carbonyl group of the 3-carboxy function, respectively. The complexes are highly luminescent and do not require luminescence enhancers. The excitation maxima of the terbium chelates are at 320 nm. The assay is based on the quenching of the hypersensitive 545-nm luminescence of the terbium complexes with the ligands 4-hydroxy-1-methyl-2-oxo-1,2-dihydro-quinoline-3-carboxylic acid (5-ethyl-[1,3,4]thiadiazol-2-yl)-amide (L(1)) and 1-ethyl-4-hydroxy-2-oxo-1,2-dihydro-quinoline-3-carboxylic acid (4-trifluoromethyl-phenyl)-amide (L(2)) by phosphate ions. The assays require equimolar (1.0 microM) concentrations of Tb(3+) and of the ligand at pH 8.0 (Tris-HCl buffer). The luminescence quenching is proportional to the concentration of aPase and CP within the range of 0.1-70 mU mL(-1) and 0.3-20 microg mL(-1), respectively. The detection limits were 0.05 mU mL(-1)=40.0 pmol L(-1) of aPase and 0.120 microg mL(-1) of CP.