The outbreak of human brucellosis among employees of a large South Australian abattoir described previously coincided with an increase in the number of cattle showing a positive serological reaction for Brucella abortus being slaughtered. Comparisons showed that two other abattoirs in the area were slaughtering larger numbers of such cattle, but no cases of human brucellosis were diagnosed there. This suggested an additional risk at the abattoir concerned. All infected men had been employed in a particular part of the works. There was a possibility of movement of aerosols, produced on opening the uteri of pregnant cattle, to other parts of the works, putting a larger number of workers at risk of infection. Modifications to the plant greatly reduced the spread of aerosols. No cases of human brucellosis were recorded at this abattoir during the summer of 1980-81.