Prior evidence suggests that endotoxin-bearing gramnegative bacteria present on raw cotton and dispersed into mill air during processing are an important cause of acute byssinosis in U.S. cotton mill workers. Examination of the literature has indicated, however, that the identity of the genera and species of gramnegative bacteria on raw cotton has been uncertainly established. Accordingly, we obtained samples of seed cotton from fields near Florence, SC, and College Station, TX, and made observations to identify the gram-negative bacteria present. Prominent among the forms isolated from the fiber were Enterobacter agglomerans, Pseudomonas syringae, and Pseudomonas VE-2. Certain other species of Pseudomonas and Enterobacter cloacae were also encounfered but less frequently. These results are considered to supplement and lend greater substance to information available in earlier reports by others. Preliminary data are also presented which suggest possible visual shortcut methods for the identification of Pseudomonas VE-2 and Pseudomonas syringae in bacterial populations from raw cotton fiber. Further work is needed to validate these shortcut procedures and to determine whether particular bacterial types tend to be dominant on the fiber in particular field exposure conditions.