Contrast sensitivity functions were measured for sinusoidal gratings from a sample of 10 anisometropic amblyopes. A high spatial frequency deficit was found from tests of the amblyopic eyes of all subjects. This defect decreased with spatial frequency and was correlated with the magnitude of anisometropia. Controls were instituted to rule out psychophysical method and residual defocus as possible causes of these effects. At low spatial frequencies, there were small differences between the two eyes. For some subjects, sensitivities of the amblyopic eyes appeared actually higher than normal whereas the reverse was found for most of the others. Additional tests demonstrated that the low-frequency differences could be accounted for by magnification differences (aniseikonia) between the two eyes. These findings are consistent with the idea that monocular contrast deprivation is the causal agent in anisometropic amblyopia.