The influence of concentration gradients upon zone migration has been investigated theoretically and experimentally. It is shown that the equation R F = A M /(α A S + A M ). is incorrect in relating the R F to the partition coefficient α. The R F shows an initial unsettled period during which it approaches a limiting R F value. Both the limiting and transient values were calculated for the migration of Methyl Orange on Whatman 3 MM paper with a water-saturated butanol solvent. Cases of radial flow with variable length wicks also treated. Using the data from rectangular flow, R R values were successfully predicted for the same Methyl Orange system. The reasons for deviation from the relationship R R 2 = R F were discussed.