There is considerable interest in thermophile microorganisms, in their environments, their ability to survive at temperatures which normally denature proteins, but more importantly, as a valuable resource for bio­ technology. The first reported isolation of Thermus by Tom Brock was in 1969. This initiated the present era of thermophilic research with the realization that where liquid water is available, there may be no limits to the temper­ ature at which microorganisms can grow. Considerable research into the ecology, physiology, metabolism, and thermostable enzymes of thermo­ philes has led to their evaluation for a range of industrial and commercial processes. The past fifteen years have been an explosive period of dis­ covery of many new genera and species, including the descriptions of a new fundamental kingdom-the Archaea. Much of the current research has been focused on the Archaea; but it is significant that during this period, the original type strain YT-l of Thermus aquaticus described by Brock has provided a major step forward in molecular biology. DNA polymerase from strain YT-I has proved to be the major success in the commercialization of enzymes from thermophilic microorganisms to date. The ease with which Thermus strains can be handled in laboratories without specialized equipment, together with the large investment in de­ scribing their structure, metabolism, and genetics, should ensure a con­ tinuing effort in Thermus research.