Nulling interferometry shows promise as a technique enabling investigation of faint objects such as planets and exo-zodiacal dust around nearby stars. At Jet Propulsion Laboratory, a nulling beam combiner has been built for the Terrestrial Planet Finder project and has been used to pursue deep and stable narrowband nulls. We describe the design and layout of the modified Mach Zehnder TPF nuller, and the results achieved in the laboratory to date. We report stabilized nulls at about the 10-6 level achieved using a CO2 laser operating at 10.6 μm, and discuss the alignment steps needed to produce good performance. A pair of similar nullers has been built for the Keck Observatory, for planned observations of exo-zodiacal dust clouds. We also show briefly a result from the Keck breadboard experiments: passively stabilized nulls centered around 10.6 micron of about 2 10-4 have been achieved at bandwidths of 29%.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.