24-hour experiments on dark-adapted compound eyes of the green lacewing, Chrysoperla carnea (Stephens) show significant daily changes in absolute sensitivity to stimuli of different colors, but no daily changes in the spectral sensitivity. The absolute sensitivity is highest for all wavelengths at mid night, and lowest at noon. The daily shift of sensitivity is, however, most pronounced in the working range of the eye in the bluegreen-green region of the spectrum. The electrophysiologically measured sensitivity of the compound eye to monochromatic stimuli correlates with the size change of its superposition aperture after illumination with white light. The daily sensitivity pattern is in good agreement with the daily flight activity pattern (see Duelli, 1986).