In situ hybridization has developed as a means of localizing specific DNA and RNA sequences within tissues. The great strength of this approach is the ability to relate the distribution of specific nucleic acids with cell structures and the protein products of the target gene by means of immunohishemistry. Complementary DNA, RNA or oligonucleotide probes, suitably labelled, are hybridized to specific DNA or RNA targets within tissues. The spatial information thus obtained has contributed greatly to our understanding of such diverse areas of research as gene mapping, viral infection, cytogenetics, protein synthesis, prenatal diagnosis and tissue grafting. This book is not intended as another recipe book, although it does describe theoretical and practical aspects of the technology. Rather, the authors critically describe the contribution made by in situ hybridization to specific areas of medical research.