The material for this work was obtained from seven eyes removed because of malignant growths. Foveal and parafoveal samples of the retinas were taken and transverse measurements were made of the absorbance spectra of the outer segments of the rods and cones, using a Liebman microspectrophotometer. Four kinds of spectra were obtained with absorbance peaks at the following wavelengths: rods, 496.3 $\pm $ 2.3 nm (n = 39); red cones, 558.4 $\pm $ 5.2 nm (n = 58); green cones, 530.8 $\pm $ 3.5 nm (n=45); blue cones, 419.0 $\pm $ 3.6 nm (n = 5). The distribution of the peaks was unimodal for the rods. For the red and green cones, however, there was evidence for bimodal distributions, with sub-population maxima at 563.2 $\pm $ 3.1 nm (n = 27) and 554.2 $\pm $ 2.3 nm (n = 31) for the reds and at 533.7 $\pm $ 2.1 nm (n = 23) and 527.8 $\pm $ 1.8 nm (n = 22) for the greens. A substantial difference in mean spectral location of the red cones was observed between patient 1 (561 nm) and patient 4 (553 nm). Both patients were classified as normal trichromats by all clinical tests of colour vision but there was a clear difference in their relative sensitivities to long-wave fields. In both direction and magnitude, this difference proved to be that required by the microspectrophotometric results.