While melt-spinning biodegradable poly-(L/D)LA 96/4 lactides into fibers, we intentionally induced monomer into the material by thermal degradation. Elevated temperatures and variable residence times were used during processing. By increasing the residence time, the molecular weight decreased, and the amount of monomer increased exponentially. The studied processing parameters induced from 0.17 to 1.24% of monomer into PLA fibers. In short-term (9-week) in vitro studies, the rate of degradation was significantly faster for fibers with higher amounts of monomer. After 9 weeks in vitro, the 0.17% monomer fiber lost 3% of its strength, whereas the 1.24% monomer fiber lost 65%. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 2996-3003, 2011