This paper will examine the transmission of secrets and related literature in London, British Library Harley MS 2558, the fifteenth-century medical notebook of Thomas Fayreford. Fayreford’s book contains, among a wide assortment of medical and surgical texts, numerous medical recipes that he collected from fellow physicians as well as from his clientele and other people he met in the course of his work as a medical practitioner. His book will serve as a case study to examine the informal communities of compilation that made up a vital area of late medieval book production. In particular, this paper will focus on a handful of recipes that Fayreford explicitly states were obtained from others or which he shared: two medical recipes for demigreyne that he received from Lady Poynyngs (one of his patients), and a friar John, respectively; and a recipe to extract a tooth using a frog that Fayreford describes as one of his “privytes”, or secrets, which he claims to have sold. The history of science in recent decades has begun to examine the social construction of science and the nature of the scientific community. Deborah Harkness, for example, focused her book, "The Jewel House", on the informal networks of exchange surrounding the study of nature in Elizabethan London. Further, there is a growing body of literature on the exchange and use of recipes and household receipt books in the seventeenth and eighteenth centuries. The work of these scholars has demonstrated that there existed explicit communities of interest and exchange in the early modern period. These sorts of communities, however, have a long and un-studied pre-history. The kind of community in which Fayreford was compiling his book is analogous and in some ways a precursor to the intellectual communities and networks of the early modern period. My paper therefore intends to bring some of this medieval pre-history to light by examining the community in which Fayreford participated and the secrets and recipes he shared and acquired within his particular community.