Human granulocytes and granulocytes from other species demonstrate differences in chemotactic responsiveness to oxidized N-formyl-methionyl-leucyl-phenylalanine.

1. Oxidation of the methionine of N-formyl-methionyl-leucyl-phenylalanine to the sulfoxide or sulfone derivative results in the loss of the peptide's chemotactic activity for human granulocytes. 2. The oxidized peptides are chemotactic for human monocytes; however, 10- to 100-fold higher concentrations are required for optimal monocyte chemotaxis. 3. Mouse, guinea pig and rabbit granulocytes, and the WBC264-9 human-mouse hybrid cell line migrated to the oxidized peptides and required 10- to 1000-fold higher concentrations of the oxidized peptides to elicit optimal chemotactic responses. 4. Human granulocytes appear to be unique in their lack of responsiveness to oxidized derivatives.