Thirteen Nigerian Upland cotton cultivars were evaluated in the greenhouse for resistance to seven new African isolates of Xanthomonas campestris pv malvacearum on cotyledons and true-leaves. Averaged over cultivars, disease grades were much lower on cotyledons (resistant) than on true leaves (intermediate resistance). Isolates of the pathogen varied in virulence. The 13 cultivars varied in resistance to the African isolates. On true leaves, ASCA(79)26 had intermediate resistance (grade 4.9) while the commercial cultivar Samaru 71 was the most susceptible (grade 8). The commercial cultivars Sairaru 71 and Samaru 77 were susceptible to isolates HV-1, HV-3, HV-5, SU-1, and CE-1. Samaru 77 was resistant to HV-6 and HV-7. The presence of these virulent isolates in the sub-Saharan countries of Upper Volta, Chad, and the Sudan is a potential threat to cotton production in Nigeria. Most of the Nigerian germplasm has the resistance genes B(2), B(3), B(9L) and B(10L) which condition resistance to the known races of the pathogen but not to the new African isolates. The multi-adversity resistance (MAR) cultivars and strains of cotton that possess resistance to HV-3 and the Sudan isolates would be invaluable in broadening the levels of resistance in the cotton improvement programs in West Africa.