Latex particles sensitized with a Salmonella O-9 monoclonal antibody were used to detect group D salmonellae in blood culture broths. The system was found to be 100% accurate when used on 104 clinical specimens that included 13 S. typhi isolates. Enteric fever could thus be diagnosed as early as 1 day after the initiation of culture in some (18%) cases. The latex particles were also used in an experimental situation to detect soluble S. typhi lipopolysaccharide by a tube agglutination method. This was found to be more than four times as sensitive as the conventional slide agglutination method because at least 50 ng of antigen per ml in either buffer or urine was detected, albeit with less efficiency when serum was used.