In the 4 years since Hammes (87) reviewed, in this journal, the application of flow and relaxation techniques to the study of primary processes in chemical reactions these methods have been applied to a wide range of biochemical problems. These applications have been facilitated by advances in stopped flow and temperature jump instrumentation, especially with respect to the range of physical properties that may be observed during a reaction, and the availability of instruments. Information about rates and mechanisms of conformational changes in polypeptides, polynucleotides, proteins, and nucleic acids have been obtained. Structural changes, from small isomerizations to major transitions such as denaturation-renaturation and helix-coil reactions, have been studied. The significance of the spectrum of conformational change for many biochemical processes is just beginning to be understood. The continued use of these and newer relaxation techniques should further merge the biological and chemical descriptions of these processes.