Improved methods are described for the isolation of pure, high molecular weight DNA from small and large scale cultures of filamentous fungi. The methods depend on the extraction of DNA under conditions which prevent nuclease activity and contamination by carbohydrate. The small scale method depends on enzymatic digestion of the wall whereas the large scale method uses partial damage followed by autolysis. High yields of DNA are obtained by both methods and the DNA is suitable for restriction analysis. Southern Blotting, RFLP analysis, dot blotting and the production of gene libraries. The small scale method can be used for the simultaneous analysis of multiple cultures.