Two diets formulated and offered for commercial fish production were examined to determine their microbial burden. The total count of aerobic bacteria ranged from 103 to 107 bacteria per gram of diet. The diets contained psychrophilic and thermophilic species and up to 104 aerobic and anaerobic spore-forming bacteria per gram. Enterococci and members of the Enterobacteriaceae, including species of Salmonella, were also present. Fluorescent pseudomonads were detected in 18 of the 47 samples tested, Proteolytic, amylolytic, lipolytic, and haemolytic organisms were shown to be present in measurable numbers. The total viable aerobic count did not change markedly on storage of representative samples at 4, 20, or 30 C.