Comparisons of the antigenic and chemical composition of pig blood and follicular fluid are reported. Follicular fluid was found to contain less protein, protein-bound orcinol-reactive carbohydrate, reducing sugar and sialic acid, but a little more acid-soluble phosphate, than blood serum. Fructose and ergothioneine were not present in appreciable amounts in either follicular fluid or blood serum. Immunoelectro-phoretic analysis showed that both follicular fluid and blood serum contained at least ten different antigenic components. Most of these were common to both but 2 of the serum antigens were not found in the follicular fluid. The follicular fluid antigen absent from serum appears to be fibrinogen. Washings from the uteri of adult non-pregnant pigs contained at least 6 antigens most of which were not found in either follicular fluid or blood.