The broad objective of this project is to identify those features of composition and structure of bacterial endotoxins that are required for expression of characteristic host reactivity. It is also considered within the scope of this framework to investigate chemically unrelated substances with endotoxin-like effects, such as polynucleotides, streptococcal peptidoglycans, and certain extracts of fungi, because this may help to elucidate the essential structural requirements for reactivity. Endotoxins are identifiable only by their pathophysiological effects; therefore, improved methods of biological assay are always sought. Current topics under investigation include the specificity of the limulus amebocyte lysate test for endotoxin, the lipopolysaccharides of Acinetobacter sp. and of oral anaerobic bacteria, and the contribution of adjuvants and carriers to active immunization of mice against virulent salmonellae.