The pH of the rument contents of cattle was recorded at slaughter; pH ranged from 5.5 to 7.8 and was not correlated with the period from saleyard to slaughter. Volatile fatty acids (VFA) were measured in 43 rumen samples; acetic, propionic and butyric were the major acids present, and the total VFA ranged from 75.9 mM/l for samples between pH 6-7, to 7.1 mM/l for samples of pH 8-9. Ten Salmonella strains belonging to 8 serotypes were grown in these 43 rumen samples. Where acid levels of these samples were high and pH low, most Salmonella sp. were inhibited; as the pH rose (pH 7-8) all Salmonella serotypes grew, some vigorously; as the total acid declined and pH continued to rise, growth of salmonella ceased. Serotypes and strains of the same serotype differed in their ability to grow in rumen contents, particularly when the pH was low.