Bacteria and other microorganisms, considered by some investigators to bear a causative relation to byssinosis in cotton millworkers, sometimes grow abundantly on cotton fiber during the process of boll opening. The extent of such growth might be expected to be greater with a slow rate of boll opening, which in turn has been seen in field observations when inadequate sunlight impinged on the boll. Not only external factors, however, but also intrinsic factors in the boll itself might affect rate of boll opening. As a first thought, we hypothesized that large bolls might open and dry at a slower rate than smaller ones. We measured rate of boll opening in terms of weight loss of detached bolls exposed either to an infrared lamp under standard conditions of temperature and relative humidity or in terms of weight loss in natural sunlight. The results showed, however, that average percent weight loss per unit time for large bolls was not materially different from that for small ones. Other factors which might influence rate of boll opening require investigation.