A prototype retractable bit system was developed consisting of a one- piece replaceable diamond set bit, a modified core barrel, bit changing tools, and surface components that allow activation of the system. Drilling with the retractable bit system is conducted in the same manner as present core drilling, except when the bit becomes worn the bit is changed with the drill string left in the hole. The operations in changing the bit are similar to those required in changing inner core tube assemblies with the wireline cable. The prototype testing indicates that this retractable bit system is feasible. It has shown reasonable reliability, but an extensive research program will be required to determine if sufficient reliability and increased productivity can be achieved to justify development of the system as a commercial product.