The "Liber Secretorum Alchimie, dating almost back to 1257, presents an attempt at introducing alchemy into the field of Aristotelian natural science (philosophy), with the purpose of providing the practice of manipulating metals with a solid theoretical foundation. Arranged from lecture notes by its author, a student of medicine originating from Pisa, it allows a direct insight into mid-13th century university teaching of natural science, which included astronomical, astrological, meteorological and geographical material. In the case of the present document, the main theological issues of the time are also passed in review. Despite the uncertainty as to the identity of the compiler of the recipes appended to its theoretical part in the 14th century manuscript, from which the text is being edited, several passages of the theoretical part of the "Liber Secretorum Alchimie also testify to the general interest of mid 13th-century intellectuals in practical proceedings. So far, little clearly datable evidence has emerged on the teaching and on the dissemination of theories on the transmutation of metals in its earlier mediaeval phase, the 13th century. This document points out that they had been taught and commented upon in lectures on Aristotle's "Meteorologica shortly after the middle of the 13th century. It also testifies to the fact that observational evidence was included in discussions at university level. The "Liber secretorum alchimie is thus the (at times rather distorted) echo of a lecture on Aristotle's writings, certainly not unlike the commentaries written by Albert the Great.