Some commercially available endotoxin assays are sensitive to both endotoxin and glucan, therefore, use of these assays will not distinguish between the Limulus amebocyte lysate (LAL) activity caused by endotoxin and that of glucan. In order to assess the contribution of glucan to the LAL activity of an organic dust, samples of lipopolysaccharide (LPS), LAL Reactive Material (LAL-RM), purified á-1,3-D-glucan, and cotton dust were evaluated using a kinetic chromogenic (ACC(c)) and turbidimetric (ACC(t)) glucan sensitive LAL from Associates of Cape Cod, Woods Hole, Massachusetts and a commercially available LAL that is insensitive to glucan (BW-Biowhittaker, Walkersville, Maryland). For LPS there was no measurable LAL response in NaOH treated samples using the BW lysate. For the ACC(c) lysate, NaOH removed up to 5 logs of LAL activity and for the ACC(t) lysate, NaOH removed up to 4 logs of LAL activity. The BW lysate was not responsive to either the treated or untreated samples of LAL-RM or á-1,3-D-glucan. For the ACC(c) lysate, NaOH reduced the LAL activity of LAL-RM and á-1,3-D-glucan by 1 log. The ACC(t) lysate was non-responsive to either the untreated or treated samples of LAL-RM and LAL responsiveness was reduced by one log in the treated á-1,3-D-glucan samples. All three of the lysates-BW, ACC(c), ACC(t-)were responsive to equivalent preparations of untreated cotton dust (297, 6872, and 1162 EU/ml, respectively). NaOH removed all activity of the cotton dust preparations when evaluated with the BW lysate. With the ACC(c) lysate up to 2 logs of LAL activity of the cotton dust preparations were removed and up to 3 logs of LAL activity were removed for ACC(t). These data would suggest that glucans are present in organic dust and the ACC lysates are sensitive to glucan. However, it appears that NaOH treatment does reduce the LAL activity of glucan and thus, at present NaOH treatment and use of a glucan sensitive lysate is not a method to qualitatively assess the contribution of glucan to organic dust.