One of the principal problems in the major cotton producing area of Brazil is the occurrence of diseases, amongst which the Cotton Blue Disease has a major impact. The symptom include a decrease in intemode length, the reduction in plant, leaf and boll size, a clearing of the leaf veins that appear darker and curved downward . The disease is caused by a Luteovirus, the Cotton Leafroll Dwarf Virus (CLDV) that is transmitted by aphids. The control of the disease relies on the control to a low level of the aphid vector, but mo t importantly on the availability to growers ofre i tant varieties. Resistance to the virus is inherited as a monogenic and dominant character. Screening germplasm for Blue Disease resistance under naatural conditions in the field is complicated by the fact that aphid infestation does not occur homogenously, which results in the possibility of escape occurring. Thu the identification of PCR-based molecular markers linked to Blue Disease resistance would be of great help to the cotton breeders in their efforts to breed disease resistant varieties .ln order to identify such molecular markers linked to the resistance gene, an interspecific (Gossypium hirsulum var. DeJtaOpal X G. barbadense MTI21) F2 mapping population was constructed. The parental genotypes were chosen such as the resistance stems from a cultivated cultivar while maximizing marker polymorphism through the use of a susceptible G. barbaden e accession. ixty-two individual plants of the F2population were used for DNA extraction and phenotyping for their response to virus inoculation, which was achieved under controlled conditions in the greenhouse by transferring infectious aphid to the plantlet . Microsatellite markers were chosen for their ability to produce clear amplification products and bands that are polymorphie between the two parental accessions. Results of the phenotyping confirm the simpIe inhcritance - a single dominant gene - of the resistance in our population, thu valida