The ratio (Hookean slope in H2O/Hookean slope at 65% R.H.), where both measurements of the Hookean slope are on the same fiber, is shown to be independent of fiber cross-sectional area, and, for a given fiber type and previous history, the fiber-to-fiber variation of the ratio is small. Since chemical treatments markedly affect this ratio, its use to detect chemical process modification of animal fibers presents attractive possibilities.