A new method for the diagnosing of leaks from liquid transmission pipelines is proposed in this paper. The solution consists in the acquiring of the new diagnostic information (i.e. the new diagnostic signals). These signals result from the operation of special testing objects joined to a tested pipeline. This paper presents the results of the application of the proposed method upon the laboratory pipeline. During experimental tests it has been determined that thanks to the use of these new diagnostic signals improving the efficiency of diagnosing of leaks is possible.