tests were performed to determine the effects of a fiber surface treatment on the interlaminar shear strength of dry and moist twaron aramid-epoxy composites. unidirectional specimens, some containing treated fibers and some containing untreated fibers, were subjected to elevated temperatures and humidities for periods of up to 14 months. periodically, the interlaminar shear strength was measured and correlated with the moisture concentration at the plane of failure, i.e., near the midplance of the specimen. the data indicated that for dry specimens, the fiber surface treatment increased the interlaminar shear strength by about 44 over specimens with untreated fibers. as the specimens absorbed moisture, their strengths decreased, in inverse proportion to the moisture concentration at the plane of failure. for a given moisture concentration at the plane of failure, the specimens with treated fibers were stronger than those with untreated fibers. however this difference in strength decreased with increasing moisture concentrations. (author abstract) 8 refs