Different cotton varieties and strains were tested for resistance to Verticillium albo-atrum Reinke and Berth, under field and greenhouse conditions. Under naturally infested field conditions, these varieties and strains were different in the percentages of plants with vascular discoloration. Under greenhouse conditions, where the plants were artificially inoculated, the varieties and strains tested had different percentages of true leaves with disease symptoms. In both experiments, the varieties IAC RM2 SM and IAC RM3 had the highest tolerance to Verticillium, while the strains IAC 13-1 and IAC 13 were the most susceptible. The other varieties tested were variable in degree of tolerance.