Treatment of milled defatted capon feathers with filtrates of Streptomyces fradiae ATCC 10745 that had been concentrated 20 times showed that the most keratin degradation in 0.5 h occurred at pH 8.0 and 60 °C. If assay time was extended, however, a decrease in reaction rate occurred and appeared to result from keratinase instability at elevated temperatures. Exposure of commercial feather meal to unconcentrated culture filtrates for 15 h produced greatest degradation at 50 °C.