Normal-state transport properties of high-T_c cuprate superconductors above T_c have been considered to be very anomalous. The resistivity ρ in the CuO_2 plane increases linearly with temperature for optimally doped samples. The Hall coefficient RH shows peculiar temperature dependence whereas the thermopower only weakly depends on temperature. It has been pointed out that these anomalous properties indicate exotic mechanisms of high-T_c superconductivity. However, recent results demonstrate that the inverse Hall mobility μ^<-1>_H=ρ/R_H obeys a universal T^2-law for various high-T^c systems. This means that ρ and R_H are highly correlated, and thus suggests a new interpretation of the normal state properties of high-T_c cuprates.
