Viable bacterial burden in a chicken shackling room used for poultry processing was investigated. Four aerosol samples were collected aerodynamically near the crate entrance with an Andersen stage sampler on trypticase soy agar. Two samples were taken in the morning and two in the afternoon on two consecutive days at the same time each day. The samples were incubated aerobically overnight at 37 degrees-C and colonies were enumerated in terms of colony forming units (CFU). Bacterial isolates were selected at random to prepare pure cultures in a differential medium which inhibited the gram positive bacteria and allowed for measurement of lactose fermenting and non lactose fermenting organisms. The CFU were examined for morphology, pigment formation, catalase activity, microscopic appearance, and staining. Samples were collected at 65 percent relative humidity, 27.8 and 22.8 degrees dry, and wet bulb temperatures. Enzyme activity was assayed under 55 percent relative humidity, 32.3 and 25.0 degrees dry, and wet bulb temperatures. Larger CFU counts were obtained in the first three stages of the sampler and the counts were higher for the afternoon samples with a mean count of 650000 CFU per cubic meter, compared to 360000 CFU for the morning samples. For the gram negative organisms, larger CFU were counted in the first three stages of the Andersen sampler at both times and larger numbers of organisms were observed than by the general purpose agar medium. The gram negative counts were higher in the morning (9700 CFU per cubic meter) than in the afternoon (6500 CFU per cubic meter). Lactose fermenting organisms outnumbered non fermenting organisms at all sample stages and times. Four gram positive species (Bacillus, Corynebacterium, Micrococcus, Staphylococcus) and five gram negative species (Acinetobacter- calcoaceticus, Alcaligenes, Escherichia-coli, Hafnia-alvei, Proteus- mirabilis) were identified. The authors conclude that high concentrations of endotoxic bacteria can be isolated at the worker's breathing zone in poultry processing farms.