This work reports the results of laboratory drilling tests conducted in order to measure improvements due to design and cutter modifications on PDC bits intended for use in geothermal well drilling. These tests, using 142.88 mm-dia. PDC full face bits, concentrated on improvements in bit life and cost performance. The tests were performed using granite drilling samples and a laboratory drilling machine at atmospheric conditions. The results from changes in bit and cutter shape are reported in the work. (C) 2002 CNR. Published by Elsevier Science Ltd. All rights reserved.