Five cows were exposed to Co6 0 irradiation which was directed to the udders or to the hind part of head. The strength of the irradiation was about 250-750 mr per week, for 7-10 days, 1-3 times during two years. The effect on milk yield, milk fat and on the oth e r physiological points was very small. An investigation on the physico-chemical properties of the milk was made, and it was found that there was scarcely any effect on the distribution of the components of the milk protein. Electrophoretic examin a tion of the skimmilk was made by the Tiselius apparatus, but there was nearly no effect. All of the cows and calves born after the irradiation have been healthy to this day, throughout 3-5 years.