The toxicity of mycotoxins to rat pulmonary macrophages was studied in-vitro. Alveolar macrophages harvested from male Long-Evans-rats were incubated with T2-toxin (149291) or patulin (149291). Toxicity was evaluated by determining the effects on viability, cell number, mean cell volume, chromium-51 release, adenosine-triphosphate (ATP) content, macromolecular (protein) synthesis, activation by lipopolysaccharides, and phagocytosis against Staphylococcus-aureus or sheep erythrocytes. T2-toxin was highly toxic to the macrophages as shown by loss of viability, release of chromium-51, inhibition of macromolecular synthesis, inhibition of phagocytosis, and inhibition of activation by lipopolysaccharides. Patulin caused a significant release of chromium-51, decreased ATP concentration, significantly inhibited protein synthesis, markedly increased mean cell volume, and significantly inhibited phagocytosis. The authors conclude that T2-toxin and patulin are highly toxic to rat alveolar macrophages as shown by their ability to inhibit several critical cellular functions. Inhaling airborne grain dust or silage particulates contaminated with these mycotoxins could have deleterious effects on normal macrophage function and pose a hazard to exposed workers.