A close relation between the state of wakefulness, the electroencephalogram, and the respiration has been demonstrated (Bülow 1963). In the present paper it was assumed that as opening and closing of the eyes influence the EEG and thus probably the state of wakefulness, the responsiveness of the respiratory center may likewise be influenced by the single act of closing the eyes. Seven subjects were studied in the steady state of rest breathing ambient air, 4-5% CO2 in air, or 11% O2 in nitrogen. In experimental periods of 4-5 minutes their pulmonary ventilation and alveolar PCO2 were measured while they randomly were either reading a book, or were blindfolded. It was found that in all three conditions closing of the eyes resulted in a mean decrease of VE of 8 to 14% with a concomitant increase of PACO2 of about 1 mmHg. It is tentatively suggested that other and stronger central or peripheral stimuli impinging on the reticular formation of the brain may explain the changed sensitivity of the respiratory center towards the chemical stimuli in conditions like exercise, chronic hypoxia etc.