Evaluation of a Tourist Agency Participation Changes in the Market (a Suggestion of New Cause Analysis Method) This article attempts at presenting the possibilities of applying a new method of cause analysis (defined by equasions 10-12) in the description of the influence of elements creating the tourist agency service volume on the market upon the origin of the difference between the agency's service volume in two moments of time. This method has been presented against the background of commonly used methods; the functional one and the one of successive substitutions. Basing on the analysis of five instances presenting the different change combinations of elements creating the tourist agency sales on the market, i.e. the proportional participation of the tourist agency in the market, the number of employees in the agency and their productiveness, some properties of the new cause analysis method have been formulated. Many advantages of this method in comparison to the ones applied so far as well as its practical usefulness while examining the elements creating the changes of the tourist agency sales on the market have been presented here.