Here we report the presence of a low molecular weight (10,000 neutrophil chemotactic factor (NCF) in the supernatants of activated human T lymphocytes. Appreciable amounts of the 10,000 MW NCF were generated by peripheral blood mononuclear cells (PBMC) stimulated with anti-CD3 antibody, and comparable NCF was secreted by both long-term human T-helper (CD4+) cell lines reactive with house dust mite (Dermatophagoides farinae) and influenza A virus-immune T-cell clones. When the cloned T cells were stimulated with specific antigen in the presence of irradiated accessory cells (AC) or insolubilized anti-CD3 antibody the 10,000 MW NCF was readily identifiable in 24-hr culture supernatants. Cultures of AC and antigen alone produced negligible neutrophil chemotactic activity, as did control cultures using an irrelevant allergen (mixed grass pollen). These findings indicate that the 10,000 MW NCF may be T-lymphocyte derived and that formation and release are dependent upon stimulation via the antigen receptor.