A Taylor dispersion method has been used to measure ternary diffusion coefficients of three-component aqueous systems, D(11), D(22), D(12), and D(21), for aqueous solutions of CuCl(2)-theophiline at temperatures of (298 and 310) K at carrier concentrations from (0.000 to 0.010) mol.dm(-3), for each solute, respectively. The results are compared with these obtained for (H(2)O + CuCl(2)) and (H(2)O + 1,3-dimethyl-7H-purine-2,6-dione), also reported here.