Abstract: A research associate at the NBS Center for Radiation Re- search has developed an improved method for measuring radiation-induced damage to specific sites in the DNA molecule.Dr. Miral Dizdaroglu uses a technique called capillary gas chromatography-mass spectroscopy to isolate and identify radiation-induced products of all four DNA bases in a sin- gle experimental run.The technique is expected to be particularly useful to re- searchers seeking to understand bio- chemical mechanisms for repairing dam- aged DNA.Changes to the four DNA bases-adenine, guanine, thymine, and cytosinewhether caused by radiation, chemicals, or natural processes, are be- lieved to play an important role in pro- cesses that cause cancer or mutation. EFERENCE MATERIALS DESIGNED FOR "THIN" SPECIMENSLaboratories that use x-ray fluorescence spectrometry for elemental analysis of "thin" specimens such as airborne pollutants or toxic par- ticles in waste water can now calibrate instruments reliably using either of two new NBS Standard Reference Materials (SRM's).Developed in cooperation with the U.S. Environmental Protection Agency (EPA), the materials were pro- duced initially to assist EPA in measuring various elemental particles from ambient air samples gathered on filters.But be- sides being used to calibrate x-ray spec- trometers, the SRM's may be used by manufacturers as a "yardstick" in the production of commercial secondary standards, which have not been traceable to an internationally recognized standard before now.Each SRM consists of a 0.55- micrometer-thick glass film deposited onto a polycarbonate filter mounted on an aluminum ring and contains known concentrations of various elements.One of the new materials, SRM 1832, is certi- fied for the concentrations of aluminum, silicon, calcium, vanadium, manganese, cobalt, and copper.Its companion, SRM 1833, is certified for silicon, potassium, ti-