The amino-terminal 98 residues of porcine vimentin have been determined by amino acid sequence studies. Extensive overlap is seen with the corresponding region of the carboxyterminal 448 residues of hamster vimentin predicted from DNA sequence studies, which left the very amino-terminal region unknown. The combined data show that contrary to gel electrophoretic results, mammalian vimentin contains only about 467 residues, and that species-specific drift occurs mainly in the amino-terminal non-alpha-helical array. The results are discussed parallel to emerging concepts on intermediate filament protein diversity.