buffy coat leukocytes Interferon-α (IFN-α) is a leucocyte-derived cytokine with pleiotropic effects on the cells of the immune system, including the ability to promote viral and microbial killing.Five batches of buffy coat  leukocytes IFN-α were prepared and purifiied from five male buffalos under the same conditions of collections ; before,during and after slaughter .  Three IFN-α doses; 200.500 and 1000 IU were prepared. The present study was designed to evaluate the biologically active dosage of aerosolized buffy coat leukocytes IFN-α, in male albino rats. Four healthy groups were included: Group 1 (control, n=10) received 0 IFN- α ,Group 2 (n=10) received 200 IU IFN-α , Group 3 received 500 IU and Group(4) received 1000 IU  / day in order to determine the minimal IFN-α dose able to induce biological effects without side-effects. Result data showed that 500 IFN- α IU/ day for five days  induced a significant biological activity, increasing serum levels of biochemical , hematological and IFN-γ levels. It is concluded that aerosolized IFN-α administration to the lung is well-tolerated at biologically active doses.