Fibers have been prepared and characterized from high-temperature capability poly mers which include the poly (benzimidazoles), poly (oxadiazoles), poly (thiadiazoles), poly (triazoles), and poly (thiazoles). The poly (benzimidazoles) and poly (thiazoles) are formed by condensation reactions and are spun directly to fibers. The poly(triazoles), poly (oxadiazoles), and poly- (thiadiazoles) are all obtained by cyclization reactions of precursor polyhydrazides. Poly(m,p-phenylene)-4-phenyltriazole was obtained from poly(m,p-phenylene) hydra zide by cyclodchydration with polyphosphoric acid, in the presence of aniline, and was spun from formic acid. Due to the insolubility of the oxadiazoles and thiadiazoles, they were spun as the precursor polyhydrazide and poly(oxathiahydrazide), respectively, followed by thermal conversion to the final form. The effect of spinning parameters on the properties of the fibers has also been investigated. Particular emphasis was directed toward the evaluation of fibers at elevated temperatures.