The objectives of this study were to determine genetics of Al tolerance and whether the Al tolerance observed is governed by the same gene. The lines 'L-7903' and 'L-4602' have been developed through breeding programme as Al-tolerant lines. These lines showed maximum root regrowth and minimum accumulation of Al and callose as compared to sensitive genotypes ('BM-4' and 'L-4147'). Al tolerance in the parents, F 1 , F 2 and backcross generations was estimated using the regrowth of the primary root after staining and scoring of fluorescent signals. The F 1 hybrids responded similarly to the tolerant parents, indicating dominance of Al tolerance over sensitivity. The segregation ratios obtained for Al tolerance and sensitivity in the F 2 and backcross generations were 3 : 1 and 1 : 1, respectively. Test of allelism confirmed the same gene was conferring Al tolerance in both genotypes ('L-7903' and 'L-4602') as the F 1 was also tolerant and no segregation of tolerant : sensitive was recorded. These results indicated that Al tolerance is a monogenic dominant trait that can be easily transferred to agronomic bases through backcross breeding technique.