Approaches to alleviate the environmental degradation of as-spun poly-p-phenylenebenzobisoxazole (PBO AS) fibers by moisture, acidic conditions, and UV-visible radiation were implemented and tested for efficacy. The general approaches tested include: extraction and neutralization of residual phosphoric acid using supercritical carbon dioxide; the use of UV-visible light blocking coatings of exfoliated graphite, carbon black, and glassy titanium dioxide; and improvement of initial fiber properties by the application of forces tending to compact the fiber microstructure. (c) 2006 Wiley Periodicals, Inc.