The effect of retrobulbar epinephrine administration on ocular and optic nerve blood flow was studied in phakic rabbit eyes using a radioactive microsphere (85Sr) technique. Blood flow measurements were performed either 5 minutes or 30 minutes after retrobulbar injection of 10μl of a 2% (base) epinephrine bitartrate solution to the right eye of each rabbit. Blood flow was determined for the iris, scraped ciliary processes, choroid, retina, and optic nerve. Five minutes after retrobulbar injection, there was no statistically significant (P>0.05) difference in eplnephrine-treated eyes compared to contralateral control eyes that received 10μl of retrobulbar saline. Thirty minutes after injection, eyes receiving retrobulbar epinephrine had a statistically significant (P<0.05) fall in blood flow to the iris and scraped ciliary processes, but not to the choroid, retina, or optic nerve.