SummaryWe analysed all major proteins secreted into culture media from Salmonella typhimurium. Proteins in culture supernatants were collected by trichloroacetic acid precipitation, separated in SDS±polyacrylamide gels and analysed by amino acid sequencing. Wildtype strain SJW1103 cells typically gave rise to nine bands in SDS gels: 89, 67, 58, 52, 50, 42, 40, 35 and (sometimes) 28 kDa. A search of the sequences in the available databases revealed that they were either agellar proteins or virulence factors. Six of them were¯agella speci®c: FlgK or HAP1 (58 kDa), FliC or agellin (52 kDa), FliD or HAP2 (50 kDa), FlgE or hook protein (42 kDa), FlgL or HAP3 (35 kDa) and FlgD or hook-cap protein (28 kDa). The other four bands were speci®c for virulence factors: SipA (89 kDa), SipB (67 kDa), SipC (42 kDa) and InvJ (40 kDa). The 42 kDa band was a mixture of FlgE and SipC. We also analysed secreted proteins from more than 30¯agellar mutants, and they were categorized into four groups according to their band patterns: wild type, mot type, polyhook type and master gene type. Virulence factors were constantly secreted at a higher level in all¯agellar mutants except a Dmot (motAB deletion) mutant, in which the amounts were greatly reduced. A new morphological pathway of¯agellar biogenesis including protein secretion is presented.