Bacterial transformation is a process of intercellular transfer of genetic information in which an extra-cellular DNA molecule can bind to competent recipient cells, penetrate the surface layers of that cell, and physically replace the homologous region of the recipient genome (Brauns, 1955). The process of transformation can be divided into two general phases: uptake and penetration of donor DNA, and recombination. Of general importance to the field of molecular biology is the elucidation of the mechanisms involved in the process of DNA transport in bacterial transformation since it may provide insights into the manner in which the surfaces of more complex cells may interact and respond to informational macromolecules in the environment. The knowledge derived from the enzymological studies proposed here, together with the information on intermediate and by-products of recombination already available, should finally provide a coherent picture of the mechanism of transformation. The primary objectives of these studies are: (a) to investigate the nature of the deoxyribonucleases involved in the processing of DNA for transport in the genetic transformation of Bacillus subtilis by examining two specific endonucleases found in competent cells, (b) to isolate mutants defective in transformation and examine nuclease levels in these organisms, (c) to investigate the mechanism of heat-activation of the magnesium-dependent endonuclease, and (d) to characterize exonuclease-defective mutants with respect to transformation.