The Sherlock Holmes stories still belong to the best-loved detective stories. There are countless studies of the master sleuth Holmes himself, but interestingly enough there is no study which deals with the structure of the stories that is partly responsible for their popularity. That is why this thesis examines the basic pattern and the variations of the detective stories by Arthur Conan Doyle. In the first part of the thesis a method for examination of the stories will be developed. Since literary studies preferred not to deal with formula literature for a long time, we do not have an adequate method for analysing literature that does not follow the patterns of "high" literature. To analyse a literary work like the Sherlock Holmes stories, new ways of dealing with formula literature have to be found. Taking a close look at the structure of detective stories shows on the one hand that they funcrion according to a strict pattern or formula, on the other hand they are game-like. Thus this thesis shows the resemblance between the basic construction of a game and a detective story. The second part of the thesis deals with the development of the detective story, therefore Edgar Allan Poe's theoretical premises for the conception of the shorz story and the construction of his tales of ratiocination (a kind of forerunner of the detective story) are analysed. Then a method for the analysis of the Sherlock Holmes stories is developed and explained. To be precise in showing according to which rules Conan Doyle's stories function, three different tables are presented which help to examine the stories on three levels regarding the particular pattern and different variations: a) characters, b) setting and elements of action and c) course of action. The third part of the thesis consists of an analysis of all 56 Sherlock Holmes stories which are analysed according to their particular varied character. Here it is shown how the typical basic structure of the stories and their extreme variations look like, how the various elements are varied and combined and which types of elements are used often or rarely. It can be shown that Conan Doyle sticks to a very strict pattern of variations which surprisingly leads - against the conviction of former studies on Conan Doyle - to many modifications on various levels. Conan Doyle is - in contrast to Poe - successful in creating a clear pattern of various elements for the detective story. The reader recognizes these elements again and again and thus is given help for orientation. On the other hand, this pattern gets modified at the same time so that the reader is always confronted with an interesting interplay of elements familiar and unfamiliar to him. It is this very interplay of basic pattern and modification which makes the stories so attractive - the variations prevent the pattern from becoming boring. We can thus say that it is incorrect to criticize Conan Doyle for using a stereotyped pattern which ended as a total cliché because this thesis' analyses show that the frame used for the stories remains very variable although it consists of constant factors. Although Conan Doyle uses a lot of typified elements, he varies their composition in every story in a new way: there is hardly a story with a low degree of variation of the elements on either the character or the setting level or the level of the course of action. We can detect a cybernetic balance on all three levels due to variation: when Conan Doyle uses a low degree variation on one or two levels, the variation on at least one other level is due to be higher. This thesis ends with a discussion of the importance of the author of the Sherlock Holmes stories for the genre of the detective story. The results of the analyses in this thesis show that not Edgar Allan Poe, but Arthur Conan Doyle is to be regarded as the founding father of the genre detective story.