By means of pO2-needle electrodes the oxygen tension in the anterior chamber of rabbit and cynomolgus monkey eyes was measured and correlated with the topography. It can be clearly shown that the pO2 in front of the pupil is substantially lower than in front of the anterior iris surface. It is evident that the O2-supply of the anterior chamber is provided by the iris vasculature. This result was confirmed by measurements after partial or total iridectomy. A brief recapitulation of the morphology of the iris showed that the abundance of iris vasculature is well understandable in view of these pO2 measurements.