DNA of 35 patients with Duchenne muscular dystrophy (DMD) from 27 unrelated families from the northern part of GDR, Czechoslovakia and Hungary were analysed by means of 9 genomic probes and cDNA probes Cf 23a and Cf 56a, which detect exons of the central part of the DMD gene. Of the unrelated DMD patients, 63% have deletions for one or more intragenic and/or cDNA probes and 33% have deletions for genomic probes, mostly for pERT 87 (15%) and P 20 (15%). 48% of the DMD patients have deletions for one or more exon regions detected by Cf 56a and Cf 23a. The deletions were mapped. The genomic probe P 20 and the distal part of the cDNA probe Cf 23a detected the same part in the centre of the DMD gene. The deletions are heterogeneous in size and extent. In patients of the same family, identical deletions were detected in the DMD gene. The detection of deletions is useful for prenatal diagnosis and carrier detection.