Recently, high levels of prorenin were found in human vitreous and subretinal fluid. In this study we attempted to identify and quantitate renin and prorenin in the bovine eye. Both these substances are present in the bovine eye in concentrations that cannot be explained by plasma contamination. Concentrations of total renin, i.e. renin plus prorenin, are highest in the posterior uveal tract [15.4 ng angiotensin (Ang) l/g per h]; in the anterior uveal tract the total renin concentration was 10.1, in plasma 6.3, in vitreous fluid 5.7 and in the retina 5.1 ng Ang l/g per h. Vitreous fluid contains mainly prorenin (99%), whereas the retina, and the anterior and posterior uveal tract contain less prorenin (respectively, 78, 47 and 32%). The absence of renin in vitreous fluid is consistent with the general finding that extrarenal renin synthesis is often associated with the release of mainly or exclusively prorenin into the extracellular fluid. Synthesis of renin and prorenin may take place in the eye.