For a number of years, researchers and others concerned with endotoxin levels in cotton lint or cotton dust have known that when identical samples are assayed for endotoxin content, level differences, often in orders of magnitude, may exist in results between laboratories. An experiment was designed in which about 10 laboratories with established endotoxin assay protocols would participate in an interlaboratory test to assay "uniform", vertically elutriated dust to gain insight into the problem. An elaborate cotton blending and dust blending and collection protocol was developed and implemented to produce this dust. The methodology is described and results on dust uniformity are reported.