Nineteen varieties of cotton, covering a wide range of fiber properties like maturity, fineness, and strength uniformity ratio were swollen in 5N KOH and NaOH at room temperature (30 +/- 1 degrees C). Tensile and fine structural properties of the resultant samples were measured and their relationship with initial fiber properties was examined. A comparative evaluation of fiber properties of KOH swollen fibers with those swollen in NaOH revealed that, irrespective of variety, fibers swollen in the former reagent retain higher tenacity. It was further noted that fine structural parameters like crystallite orientation and amorphous content which influence tensile properties become modified differently while swelling in the two reagents. While changes in crystallite orientation were found to be less drastic during KOH swelling, unlike in NaOH, the reverse was found to be true with crystalline content. These changes in fine structure could more or less explain the variation in tensile properties of fibers swollen in these two reagents.