The effect of ammonium perchlorate supplementation in a dose of 1gm/100 kg body weight was studied on 10 Freisian cows for 5 months. Milk yield was studied and milk samples were taken to determine some milk constituents. At the same time blood samples were taken for the examination of the blood picture. Our results showed that giving ammonium perchlorate caused significant increase in milk yield with relative increase in its fat %. Variation in the other milk constituents were within the normal limits, except the significant decrease of immuno-glo bulin. Examination of the blood revealed the presence of signifi cant increase in the total count of RBCs, WBCs, Hb conten ts, PCV% and lymphocytes%. In addition to these, there was relative decrease in the percentage of neutrophils.