In order to establish a system for gene cloning in the ergot fungus Claviceps purpurea mitochondrial DNA was purified from two wild strains and four descendants of production strains. A characterization of the mt DNA with respect to buoyant density, molecular weight (45 kb corresponding to acontour lenght of 14 μm) showed no differences. However, considerable differences were detected in the restriction pattern, with the exception of two commercial strains of possibly common origin. From this it follows that restriction patterns of mt DNA may be used as finger prints to identify related strains.In one of the wild strains plasmids associated with the mitochondria were found. A characterization of two species p11 and p12 having molecular weights of 6.6 and 5.3 kb revealed that these genetic units are linear having respective contour lengths of 2.1 and 1.7 μm. According to Southern blot analyses both plasmids show homology to each other, but not to the mitochondrial "chromosome". Accordingly, p11 and p12, despite localization in the mitochondria, are evidently not an integral part of the mt "chromosome". The possibility to use the mt DNA and mitochondrial plasmids to establish a vector system for molecular cloning in imperfect strains of Claviceps purpurea has been pointed out.