The relative viscosity (eta(r)) and the viscosity B-coefficients in the equation eta(r) = 1 + Be + Dc(2), with c = concentration of 18-crown-6 (18C6) in aqueous and carbon tetrachloride solutions (0.02 to 0.3 mol L-1), have been determined in the temperature range (293.15 to 308.15) K and at ambient pressure. The values of the B- and D-coefficients are found to be high compared to those obtained for simple nonelectrolyte solutions. These values are further found to decrease and increase, respectively, as a function of temperature in aqueous solutions, while the value of the B-coefficient remains more or less constant in the case of CCl4 solutions in the studied temperature range.