Food mycotoxin deoxynivalenol (vomitoxin, DON) produced by Fusarium graminearum and F. culmorum can induce rapid diminution of lymphoid tissues and lymphopenia in the growing chickens and mammals. We first investigated the direct acute effects of DON on the chick immune-related embryo tissues such as embryonic liver and spleen. Direct DON administration into the embryonic eggs caused toxin accumulation in liver in a time-dependent manner. Electron microscopic observation showed a notable accumulation of fat droplet in the liver tissue and the re-exposed hatched chicken showed more distinguishing enlarged fat globules, so-called fatty cysts like human steatosis. Regarding effects of deoxynivalenol on the chick embryonic spleen, fatty change was also observed in splenocytes. Functionally, mitogen-stimulated cellular and humoral lympho-proliferations were suppressed in the DON-treated embryo. Conclusively, acute direct exposure to deoxynivalenol in the chick embryo caused toxic histological alterations in the liver and spleen and suppressed in vitro lymphoblastogenesis.