A computerized instrument, an on-line electro-optic relaxation spectrometer, has been developed and is being used to study the motions of DNA macromolecules. The macromolecules in solution are exposed to an electric impulse, and their responses are measured by means of a polarized light beam and photomultiplier cell, which gives a time dependent electrical signal. The signals are sampled electronically, digitized, and displayed on an oscilloscope, chart recorder, and at the output of a computer. The computer and special programs are used to analyze the signals (which may be birefringence, dichroism, or fluorescence) and to fit them to mathematical functions for further interpretation in terms of models and mathematical theories. Calf thymus and bacteriophage and plasmid DNA's are being studied, including superhelical forms. The effects of various binding agents - mutagens, carcinogens, and antitumor drugs - on DNA structure and flexibility are being determined. The objective is to find out how these substances interact with DNA and influence genetic processes.