Twenty settled and 69 respirable grain dust samples were collected from 5 grain elevators along the lower Mississippi River. Studies were performed on 2-keto-3-deoxyoctonate (KDO) concentrations, total bacterial plate counts, gram-negative bacteria (GNB) count, identification of GNB, and endotoxin levels. KDO values were 52.1-510.0 ng/mg. A new method involving gas liquid chromatography was developed to analyze for KDO. No correlation could be made between KDO and endotoxin levels. Total bacterial plate counts for settled dusts ranged from 1.9 to 53.4 million/g, while the GNB count was 0.1-50.0 million/g. Two hundred and thirty GNB were isolated from all samples and identified. Sixty-one percent were Enterobacter agglomerans, followed by species of Pseudomonas (9.1%), Serratia (6.9%), Actinetobacter (6.9%) and other genera (16.2%). All but four of the airborne samples had no significant bacterial population. Twenty-three of sixty-nine airborne samples contained 0.6 ng of endotoxin while 3 filters had 6.0 ng. All settled dust samples were contaminated with endotoxin at levels ranging from 22.5 - 187.5 ng/mg. Based upon airborne endotoxin levels worker exposure range was extrapolated to be 0.0-0.2 ng/kg body weight per 8 hr period. This is much less than that necessary to elicit febrile and pulmonary responses. However, the heavily laden filters corresponded to an endotoxin dose of 1.6 ng/kg body weight.