Membrane Computing is a recent area of Natural Computing, a topic where much work has been done but still much remains to be done. There are some applications which have been developed in imperative languages, like C++, or in declaratives languages, as Prolog, working in the framework of P systems. In this paper, a software tool (called SimCM, from Spanish Simulador de Computacion con Membranas) for handling P systems is presented. The program can simulate basic transition P Systems where dissolution of membranes and priority rules are allowed. The software application is carried out in an imperative and object-oriented language - Java. We choose Java because it is a scalable and distributed language. Working with Java is the first step to cross the border between simulations and a distributed implementation able to capture the parallelism existing in the membrane computing area. This tool is a friendly application which allows us to follow the evolution of a P system easily and in a visual way. The program can be used to move the P system theory closer to the biologist and all the people who wants to learn and understand how this model works.

P system, Parallelism, Simulation, Java