The distribution of [14C]-clonidine in the eye after intravenous administration and injection into the external carotid arteries was studied in a comparative manner in anesthetized cats. The amount of clonidine accumulated in the eye after intraarterial administration by far exceeded that after intravenous application. In addition the pharmacological effects of clonidine obtained by these two routes of administration were investigated and analyzed. The decrease in intraocular pressure after intravenous administration appears to be much stronger than after intraarterial injection. Obviously, there exists no direct correlation between the clonidine concentration in the eye and the ocular hypotensive effect of this drug.