Weekly samples of cotton leaf, bract, fiber, and soil were taken during the 25-week growing season of 1985 at the Southern Regional Research Center, New Orleans, Louisiana. Total and gram-negative bacterial populations were determined. Identification of gram-negative bacteria and measurement of endotoxin concentrations were performed. Both types of populations remained relatively stable until senescence and, later, frost resulted in higher counts for each. Various Pseudomonas sp. were the predominant types present on the plant parts, with Enterobacter agglomerans the second most common. Senescence affected bacterial populations on the cotton plants, with some bacterial types increasing and others decreasing after senescence. Statistical analysis partitioned by sample type showed strong correlations between certain microbial and environmental variables with endotoxin levels. Gram-negative bacterial count was the most accurate predictor of endotoxin levels. The multiple regression of endotoxin on environmen...