Plantain, one of the main food sources for the people of central Africa, is subject to numerous production constraints due largely to numerous pests and diseases, including black leaf streak disease (BLSD, caused by the ascomycete fungus Mycosphaerella fijiensis Morelet). This is regarded as the most serious leaf spot disease of bananas throughout the world (Pasberg-Gauhl et al. 2000) and can cause very heavy yield losses depending on the epidemiological situation (Stover 1983, Fouré et al. 1984, Mobambo et al. 1993). In commercial plantations, its control requires the intensive use of fungicides which are very harmful to the environment and which increase production costs. Hence it is impossible to use this method in low-income smallholdings. As cultural techniques such as deleafing do not provide effective control, the development of plantain hybrids resistant to BLSD is vital to improve the productivity of these farms (Tomekpé et al. 1998, 1999). For several years the genetic improvement programme of the Centre Africain de recherche sur bananes et plantains (CARBAP) has concentrated its efforts in this direction. The plantain tetraploid hybrid 'CRBP-39' (Musa cv. AAAB, ITC1344), obtained by crossing a triploid female plantain (Musa cv. AAB, local variety 'French clair') and a diploid male banana M53, a synthetic hybrid (AA), is one of the results of this work. The first tests of this hybrid have shown its excellent resistance to BLSD, its good agronomic qualities and its acceptability to the people of Cameroon (Tomekpé et al. 1999). However, although tests of resistant hybrids are often made by comparison with their parents treated against BLSD (Vuylsteke et al. 1993), they are made less often with an extra comparison with an untreated parent to determine the influence of the BLSD resistance on the performance of the hybrid (Mobambo et al. 1993). The experiment which has been set up and is described here has therefore two aims: to confirm the performance of 'CRBP