Muriate of potash (100 lb/A) was applied annually from 1986 through 1989 to field plots that contained medium to low level of available potassium. Other plots were not fertilized. During 1989, 20 cotton cultivars developed beltwide in the U.S. were grown in these plots. The objective of the study was to determine the response of the cultivars to levels of potassium. Data indicated potassium level in the fertilized plots increased over the test period. Potassium delayed the onset and the severity of foliar symptoms of Verticillium wilt and the Verticillium wilt-potassium deficiency syndrome symptoms. Plant height, lint yields, and fiber quality were increased by potash application. Significant differences were obtained among the cultivars for most parameters measured. However, the lack of significant differences for cultivar x potash interaction indicated that all cultivars responded similarly to the levels of soil potassium.