Summary. The proteins in follicular fluid from individual and pooled bovine follicles were studied by gel chromatography and quantitative immunoelectrophoresis. The mean protein concentration was 86·4% of serum; very large proteins were present in only low concentrations. A minimum of 40 individual proteins was distinguished in follicular fluid, and 15 of these proteins were quantitated. A correlation between molecular weight and follicular fluid:serum concentration ratio was found. Fluid from individual follicles differed only in the relative concentrations of small and large proteins. An exception to this was IgG which was occasionally, but never in healthy growing follicles, present in concentrations above 150% of serum. Healthy growing, preovulatory and atretic follicles had higher, and cystic follicles mostly lower, concentrations of small proteins than serum. The concentration of α2-macroglobulin in healthy growing follicles never exceeded 16% of serum. The concentration of large proteins in follicular fluid increased with increasing follicle size.
Attempts to detect proteins specific to follicular fluid by immunizing rabbits with pooled follicular samples and the follicular fluid proteins not bound by anti-bovine antiserum resulted in production of antibodies against fibrinogen and its split products D + E only.