Nadolol 20 mg was administered orally as a single-blind, single dose to nine patients about to undergo cataract extraction. Intraocular pressures fell by a mean of 24% 3 h after administration. During the operation, aqueous humour and serum samples were taken for measurement of nadolol concentrations. Aqueous nadolol concentrations ranged from 3.8 to 13.4 ng ml-1, and correlated with the serum drug concentrations (r = 0.84). The fall in intraocular pressure did not correlate with either the aqueous humour or plasma concentrations of nadolol.