Nitric oxide has long been considered exclusively as a toxic air pollutant. It is now known that this gas is produced by body cells. The gaseous signalling molecule is involved in diverse functions such as cell communication in the brain, regulation of blood pressure and penile erection. The most important receptor of nitric oxide is an enzyme that produces the signalling molecule cyclic GMP. We and others have identified and localized the respective genes and have characterized the resulting enzyme isoforms. Specific subtypes associate with specific targeting proteins within cells or are expressed in an organ specific manner. One major idea behind our research is to exploit this diversity in nitric oxide receptors for the development of novel specific drugs for single receptor subtypes with novel fields of application and a favourable side effect profile. The novel classes of drugs under development may provide new treatments for cardiovascular and neurodegenerative disorders, erectile dysfunction and osteoporosis, thus having the potential to significantly enhance the quality of life of patients suffering from these diseases.