Two naturally occurring races of theFusariumwilt or Panama disease fungus,F. oxysporumf.cubense(E.F.S.) Snyd. and Hans., have been identified. Race 1 is world-wide in distribution and attacks certain AAA triploids ofMusa acuminata, of which variety 'Gros Michel? is the most important, andMusa textilis. Race 2 has been identified in Honduras, El Salvador, Puerto Rico, Virgin Islands, and the Dominican Republic and attacks certain ABB triploids ofM. acuminata×M. balbisianaknown as 'Chato', 'Bluggoe', 'Rulo', or 'Chamaluco'. Both races are pathogenic on 3- to 4-month-old seedlings ofM. balbisiana, M. schizocarpa, andM. acuminatassp.banksii, but the race 2 clone was less pathogenic than the race 1 clones tested. MatureM. balbisianais immune to rhizome infection in the field. 'Odoratum' and 'Inodoratum' cultivars ofF. oxysporumf.cubenseare found within race 1; only the 'Inodoratum' cultivar is found within race 2. Circumstantial evidence indicates an independent development of race 2 in different areas. Race 2 wilt-susceptible ABB triploids hybridize and set seed with pollen from diploidM. balbisiana(BB) andM. acuminata(AA), the two ancestors of the cultivated banana. This will facilitate a study of the inheritance of wilt resistance toF. oxysporumf.cubenseraces 1 and 2.