The activity of four recombinant human cytokines on porcine neutrophils was evaluated. Porcine neutrophils were treated with varying doses of recombinant human tumor necrosis factor-alpha (rHu-TNF), interferon-gamma (rHu-IFN), interleukin-8 (rHu-IL-8), or granulocyte-macrophage colony-stimulating factor (rHu-GM-CSF). The function of treated neutrophils was compared with that of non-treated controls in the following assays: antibody-independent neutrophil cytotoxicity (AINC), antibody-dependent cell-mediated cytotoxicity (ADCC), iodination, Staphylococcus aureus ingestion, cytochrome C reduction, random migration, and chemotaxis. Treatment with rHu-TNF produced significant (P < 0.05) depression of neutrophil random migration (2.5, 25, and 250 ng ml⁻¹ rHu-TNF) and iodination (250 ng ml⁻¹) and a near significant (P = 0.08) depression in ADCC (250 ng ml⁻¹). Treatment with 25 000 U ml⁻¹ of rHu-IFN caused a significant increase in AINC. At lower doses of rHu-IFN, there was a trend (0.05 < P ≤ 0.08) toward depression of AINC (250 U ml⁻¹) and ADCC (25 U ml⁻¹) and enhancement of iodination (250 U ml⁻¹). Treatment with 50 ng ml⁻¹ of rHu-IL-8 caused a near significant increase (P= 0.06)M in AINC. There were no significant differences noted when porcine neutrophils were treated with rHu-GM-CSF (2.5–2500 U ml⁻¹). No synergism was noted between rHu-TNF and rHu-IFN.