SOAP has been widely adopted as a simple, robust and extensible XML-based protocol for the exchange of messages among web services. Unfortunately, SOAP communications have two major performance-related drawbacks: i) verbosity, related to XML, that leads to increased network traffic, and ii) high computational burden of XML parsing and processing, that leads to high latency. In this paper, we address these two issues and introduce a novel framework for Differential SOAP Multicasting (DSM). The main idea consists in identifying the common pattern and differences between SOAP messages, modeled as trees, so as to multicast similar messages together. Our method is based on the well known concept of Tree Edit Distance, built upon a novel filter-differencing architecture to reduce message aggregation time, identifying only those messages which are relevant (i.e., similar enough) for similarity evaluation. In addition, our technique exploits a dedicated differencing output format specifically designed to carry the minimum amount of diff information, in the multicast message, so as to minimize the multicast message size, and therefore reducing the network traffic. The battery of simulation experiments conducted to evaluate our approach shows the relevance of our method in comparison with traditional and dedicated multicasting techniques.