To compare the functional T-cell avidity of HLA-A*02-restricted Tax 11–19-specific CTLs and HLA-A*24-restricted Tax 301–309-specific CTLs, patients were selected from either HLA-A*02-positive or HLA-A*24-positive HAM/TSP patients, with relatively high CTL frequencies over 0.5%. This evidence concerns the gene HLA-A and tropical spastic paraparesis.