Foliar potassium nitrate (KNO3) applications can correct late season K deficiencies. Adjuvants may promote absorption of foliar-applied nutrients, reducing nutrient loss and enhancing yield. The objective was to determine if applying an adjuvant with foliar KNO3 on medium-to-high-K soils is economically beneficial to cotton producers. Experiments were conducted between 1992 and 1995 on no-tillage cotton produced on a high-K Collins silt loam soil at Jackson, TN, and in 1993 and 1994 on conventional- and no-tillage cotton produced on a medium-K Loring silt loam soil at Milan, TN. Treatments were non-foliar check, foliar KNO3, and foliar KNO3 plus adjuvant. Foliar treatments were applied four times at 4.1 kg K ha-1 (11.2 kg KNO3 ha-1) in 94 L H2O starting at flowering to 14 d after flowering on a 9-to-14-d interval. The adjuvant was added to the foliar solutions at 1.25% (v/v). Partial budgeting was used to estimate net revenue differences ($ ha-1) among the treatments. Cost of KNO3 was $27.33 ha-1, the adjuvant, $17.34 ha-1, and machinery and labor costs for foliar application summed to $22.95 ha-1. Yields did not increase sufficiently to cover the higher cost of the foliar KNO3 treatment compared with the check. The foliar KNO3 plus adjuvant treatment, compared with the check, increased yields 70 kg ha-1 for Jackson, 52 kg ha-1 for the conventional-tillage at Milan, and 112 kg ha-1 for the no-tillage treatments at Milan, causing net revenues to increase $35.98 ha-1 at Jackson, $9.34 ha-1 for conventional till at Milan, and $98.14 ha-1 for no-till at Milan. Results indicated that no-tillage cotton producers who farm medium-to-high-K soils could increase net revenue by applying foliar KNO3, but only if the adjuvant is applied with it. Results were less convincing for conventional-tillage cotton.