This thesis is a presentation of ‘A Leche’, a deontological text in Cambridge, Gonville and Caius College MS 451/392, pp. 20-22. The title is mine. The manuscript is mentioned by Kari Anne Rand in volume 17 of The Index of Middle English Prose (henceforth referred to as IMEP), and some of the texts in the MS are commented on briefly there. However, no edition exists of any part of the MS. The text on pp. 20-22 is of particular interest because of the contents, and deserves closer attention. This thesis may be seen as a preliminary study to an edition, perhaps in the form of an article. The MS is a compilation which mainly contains various kinds of medical recipes in Latin and English. The compilation may have been puttogether much later than the time of writing, but someone must have had an interest in collecting all these texts. It looks like a typical leechbook which may have been owned by a practitioner of medicine, or someone literate and interested in medicine who wanted to be able to cure simple illnesses in his family or close surroundings. The MS is not marked by any owner or scribe, nor is there a date. M.R. James dates it to the fifteenth century, however. This thesis has three aims. The first is to place the text historically, looking more closely at both medical practice and medical writing in late medieval England. The categories of both practitioners of medicine and of writings which are defined as medical in this period are indisputably wide, demanding sub-categorisation and explanations. The subject of the text is of a deontological nature, dealing with the patient-practitioner relationship. The text gives advice on how a leech should behave towards his patients. This provides us with an interesting starting point, as texts of this kind are comparatively rare. Another aspect worth noting is the fact that unlike almost all medical texts in the English vernacular from this period, the text has no obvious Latin source.As the scribe is unknown, a second aim of the thesis is to try to localise him and place the MS geographically using A Linguistic Atlas of Late Middle English (henceforth referred to as LALME). Although it is difficult to find the exact geographical origin of a MS based solely on the spellings it contains, there should be a chance of narrowing the localisation down to a fairly restricted area.The third aim is to present a semi-diplomatic transcription of the handwritten text. I have also included a translation into present-day English, in the hope that this will make the text and its contents accessible to more scholars. Special features of the hand are commented on, along with rare spellings used.Part one of the thesis is devoted to the first and second aim, placing the MS both historically and geographically. Chapter 1 introduces the MS, with a technical description and with information about the contents of the whole collection and the deontological text in particular. Chapters 2, 3 and 4 will explore the historical context and thus provide background information for the rest of the thesis, dealing with medical education and practice, medicalwriting, and medical deontology in late medieval England. Chapter 5 presents characteristics of the scribal hand and a dialect study based on LALME to find a geographical origin for the text. Lastly, chapter 6 sums up the contextual findings in an attempt to discover more about possible users and the scribe of the text.Part two is concerned with the third aim of the thesis, presenting a transcription of the text. Chapter 7 includes notes and principles for the semi-diplomatic transcription, a facsimile of the original MS, and the transcription itself. Chapter 8 presents a translation into presentday English. Appendices are also included to provide more detailed data resulting from the research for the various sections.