The inheritance of fiber properties was studied in four germplasm lines of cotton, Gossypium hirsutum L. tolerant to Heliothis virescens Fab., tobacco budworm. Fiber properties of strength, elongation, and fineness are available in these cotton lines which may be useful in improving the fiber quality of upland cotton; however, nothing was previously known about how these lines perform in crosses with upland. The four germplasm lines were each crossed with Stoneville 213; an adapted cultivar. Generation mean analysis was used to determine the genetic effects relative to fiber properties of micronaire (fineness), 2.5 and 50% span length, elongation, and, strength. In addition to tolerance to tobacco budworm, some or all of the four germplasm lines, M-DH-118, M-DH-121, M-DH-126 and M-DH-128 have finer, shorter and stronger fiber with higher elongation. In crosses with all four M-DH lines, additive genetic effects predominated for most fiber traits, suggesting that early-generation selection should be effective. On the other hand, significant dominance effects for fiber length in all crosses and dominance effects for strength in the M-DH 126 hybrids, suggest other breeding strategies. Nevertheless, there does not appear to be any major problems associated with fiber properties in using these germplasm lines to improve tolerance to tobacco budworm. The use of these lines as parents with Stoneville 213 to produce F₁ and F₂ hybrids is also a feasible approach to breeding. Fiber properties of certain hybrids were significantly better than those of Stoneville 213. These hybrids could combine improved fiber properties with tolerance to tobacco budworm and acceptable yield in certain F₁ or F₂ combinations.