30 strains isolated from clinical cases and a laboratory induced R-mutant or S typhi were studied. The synthesis of Colicin V, Siderophores, hydroxamate and phenolate (Aerobactin and Enterochelin) were investigated using biological assays. All strains were positive for Enterochelin but only strains 6586 and 4448 were positive for Aerobactin. An 80 kD receptor for enterochelin was found in the outer membrane of strains. Only strains 4448, 635 and 4693 produced Colicin V. Plasmid related antibiotic resistance was demonstrated in 7 strains and was considered "cryptic" in 3 others. The LD50 for mice ranged from 2.7 x 10(4) to 1 x 10(9) bacteria per ml. The presence of pathogenic factors was not related to the LD50.