High-resolution transmission electron microscopy has been used to investigate disordered structural intergrowths in lead-arsenic sulfide minerals that occur at Lengenbach, Binntal, Switzerland. Most of the material examined was found to be perfectly ordered; however, some highly disordered specimens were found. The “disordered liveingite,” compositionally intermediate between dufrenoysite and liveingite, was found to be a disordered intergrowth of sartorite-like units and dufrenoysite-like units. The sartorite-like units are similar to those found in baumhauerite, whereas the dufrenoysite-like units are similar to those in liveingite. This disordered intergrowth represents a transitional stage in the replacement of dufrenoysite by the more As-rich mineral liveingite. The origins of the lead-arsenic sulfide minerals at the Lengenbach deposit are discussed; two paragenetic sequences are proposed to account for the formation of these minerals.