Although organic semiconductors have received the most attention, the development of compatible passive elements, such as interconnects and electrodes, is also central to plastic electronics. For this, ligand-protected metal-cluster films have been shown to anneal at low temperatures below 250 degrees C to highly conductive metal films, but they suffer from cracking and inadequate substrate adhesion. Here, we report printable metal-cluster-polymer nanocomposites that anneal to a controlled-percolation nanostructure without complete sintering of the metal clusters. This overcomes the previous challenges while still retaining the desired low transformation temperatures. Highly water- and alcohol-soluble gold clusters (75 mg ml-1) were synthesized and homogeneously dispersed into poly(3,4-ethylenedioxythiophene) to give a material with annealed d.c. conductivity tuneable between 10(-4) and 10(5) S cm-1. These composites can inject holes efficiently into all-printed polymer organic transistors. The insulator-metal transformation can also be electrically induced at 1 MV cm-1, suggesting possible memory applications.