Salmonella typhimuriumincreased in virulence during growth in an acid environment whereas in a near neutral environment, the reverse was true. The lipopolysaccharide content of acid- and alkaline-grown cells remained relatively constant during growth, but that in neutral-grown cells decreased. The crude endotoxin extracted from acid-grown cells was slightly more toxic than that extracted from either neutral- or alkaline-grown cells. Based on these results, any attempt, therefore, to correlate a hazard to public health with the numbers ofSalmonellapresent in a food would at this time be impossible.