The genetic interaction between two dominant, non-allelic loci which impart extreme phenotypes for hair density in upland cotton was investigated. The gene T(1) imparts dense pubescence on leaves and stems, and places hairs on the capsule. T(2)(arm) reduces hairs to the margins of the leaves (glabrous plant phenotype). An inheritance model based on interaction between T(1) and T(2)(arm) was devised. This model predicts the frequencies of phenotypes for leaf trichome density in progeny from self-pollinated T(1)t(1) T(2)(arm)t(2) plants to be 3 glabrous, 3 "normally pubescent", and 10 densely pubescent. An F₂, a BC(1) population (t(1)t(1) T(2)(arm)T(2)(arm) X F₁), and F₂-derived F₃ lines were used to test the model. No significant deviations from expected ratios were found, and all predictions were met. Therefore, T(1) is epistatic on T(2)(arm) when phenotypic classes are limited to the presence and absence of trichomes on the leaves or when T(1) is homozygous and T(2)(arm) is heterozygous. In all other situations, T(2)(arm) is epistatic on T(1). These results revise an earlier inheritance model for the interaction of T(1) and T(2)(arm).