An instrument is described for the measurement of the dichroism produced in solutions of macromolecules by pulsed electric fields. Measurements can be made with monochromatic radiation in the wavelength range from 240 to 600 nm. The pulse generation equipment employed is similar to that used by previous workers but the optics and signal detection system are novel and allow a direct measurement of the dichroism. The relation between the output signal of the apparatus and the dichroism of the sample is derived. Representative experimental data from a study of tobacco mosaic virus are presented to demonstrate the performance of the apparatus. Limitations of the instrument are noted and possible improvements are discussed.