In order to have a better understanding of the behaviour of several commercial cotton varieties in relation to the main diseases in the cerrado vegetation area, 4 trials were conducted at COODETEC's experimental station in Primavera do Leste, state of Mato Grosso, during the 2003-2004 growing period: EGTRA (Trial on the degree of tolerance to Cotton rust Ramularia); EGTDA (Blue Disease); EGTRO ("Ramubse"), and EGTPC (Boll rot). Two plants were artificially inoculated with "Ramulose". For EGTRO and all other trials, infestation took place naturally. Each trial is composed of the materials to be tested: IPR 96, IPR 94-227, IAC 24, CD 405, DELTAOPAL, IAN 338, CD 408, CD 409, and CD 410, together with a susceptible and a resistant check variety. In the case of EGTDA, the initial stand of IAC 24 was significantly reduced, and IPR 94-227 was the most tolerating variety. For EGTPC, IAN 338 was the material that underwent the most intense rotting process, and CD 409 and IPR 96 were the most tolerant to rotting. For EGTRA, IPR 96 achieved the best mark. In the case of EGTRO, CD 410 was the material most sensitive to "Ramulose" and IPR 96 and CD 407 were the most tolerant varieties after the tolerant check variety BRS Antares.