An in vitro peripheral lymphocyte blastogenesis system was used to investigate the biological activities of the fungal toxin fusarochromanone (TDP-1) and its monoacetyl derivative TDP-2. Briefly, cultures of human or bovine peripheral lymphocytes were exposed to TDP-1 or TDP-2 and a mitogen (PHA, Con A or PWM). After a standard incubation time, cell proliferation was quantified using the MTT bioassay. Human and bovine lymphocyte proliferation was inhibited by high concentrations of TDP-1; however, bovine lymphocyte proliferation was significantly increased at low concentrations of TDP-1. TDP-2 has similar but less pronounced effects on lymphocyte proliferation.