The history of the discovery and development of drugs is replete with examples where chance and "serendipity" have resulted in important advances of knowledge. In the case of nitroglycerin it can be shown that what appears to have been a chance discovery was actually the result of a sequence of selective perceptions by, and cognitive processes in individual researchers. The sources allow insight into various stages of the development of nitroglycerin, starting with the chemical synthesis as an explosive in 1846 and the first use in humans in 1847 to the discovery of a useful coronary drug. Homeopathic medicine contributed significantly to this process. Thus, the history of nitroglycerin is an example of an exchange of knowledge between otherwise separate realms of sectarian and orthodox medicine in the second half of the 19th century.