SUMMARYThe object of this paper on the Danish zoologist Henrik Krøyer is to show, from archival evidence, that he is a good example of a person who practised international communication between scientists, especially from Denmark and Germany, in the field of natural science during the 19th century. As an explorer, whose very interesting diaries are preserved, and as a pioneer of and author (in Danish) of works on marine zoology; as the founder and editor of the scientific periodicalNaturhistorisk Tidsskriftand as a correspondent with colleagues, mainly in Germany, Krøyer played an important role, which is still not sufficiently esteemed. It has been my intention to add some new perspectives to his image. His works should to a greater extent be recognized as masterpieces, even in view of modern biological problems and questions, because they combine exact descriptions not only with biological/ecological scholarship, but also with historicocritical and statistic elements. Furthermore, I plead for the publication of his not yet edited diaries, particularly those from his scientific journey