Methods are described for the measurement of the lateral chromatic aberration and distortion of microscope objectives and eyepieces. Measurements have been made on 20 apochromatic microscope objectives of 4 different makes, and on 10 compensating eyepieces of 2 different makes. The results show that the compensating eyepieces in general do not entirely compensate the chromatic aberration of the objectives and that the complete microscope system is usually undercorrected. The bearing of this on the performance of the system in photomicrographic work by a three color process and in the direct visual observation of objects is considered in detail.