Three mutations which eliminate specific types of photoreceptors in Drosophila were characterized. Of the eight photoreceptors in each facet, two mutations delete the outer six (R 1-6). The third eliminates R 7, one of the two central photoreceptors. Double mutants can be constructed in which only photoreceptor R 8 is present. The spectral sensitivities, photopigments, and behavioural properties of these mutants were investigated. R 1-6 have two sensitivity peaks, near 350 and 470 nm. These receptors contain a rhodopsin with these absorption peaks. It interconverts with a metarhodopsin that absorbs around 570 nm. R 7 is a U.V.-receptor, containing rhodopsin that absorbs around 370 nm and interconverts with a metarhodopsin which absorbs around 470 nm. R 8 is a non-adapting blue-receptor with a third type of rhodopsin. The properties of these photopigments explain the different sensitivities and spectral adaptation phenomena of the various photoreceptors. All the photoreceptors have input into phototaxis. Spectral analysis of this behaviour provides evidence for integration of the input from the different photoreceptors.