A simple and useful method to illustrate the amino acid variability of homologous proteins has been developed.In this method, called the variation Index method, a degree of amino acid variability is expressed by the Variation Index (VI) with an arbitrary unit. The VI value is calculated from the sample number and the maximum number of frequencies of different amino acid species which occurred at each positions of the aligned sequences.
The profile of the moving average of VI along the sequence show the conservative and variable regions of homologous proteins clearly.