The term molecular radiology intermediate region between radiological imaging and interventional radiology on the one side and molecular biology on the other. In the field of imaging methods are currently being developed by which molecular processes, i.e., gene expression and protein function, can be visualized in vivo. These techniques open new perspectives for research and clinical diagnosis and will be presented in the second part of this review. The present part provides a survey of current developments in gene therapy from a radiological point of view and highlights the part that our specialty may play in this field.