Amounts of sheep serum protein between 60–400 μg. albumin and 20–250 μg. γ-globulin were separated electrophoretically in Polyacrylamide gel. Within these limits there was a linear relationship between the amounts of each protein and corresponding peak areas produced by the absorption of ultraviolet light. The method was used to study seasonal changes in the composition of serum proteins in Blackface ewes. A fall in the γ-globulin content of the serum of breeding ewes of 0·063 g. per 100 serum per week during the latter half of pregnancy was followed by a rise of 0·072 g. per 100 ml. serum per week during each of the 10 weeks of lactation and each of the 4 weeks following weaning.