A computer program to check structural identifiability of biological compartmental systems, that is the priori possibility of estamating all unknown system parameters through a multi input-multi output tracer experiment is presented. The procedure, as based only on the adopted compartmental structure and the chosen input-output experiment, is independent of the numerical values of the parameters: therefore the program can be usefully employed before parameter estimation algorithms, to assure that all the unknown parameters evidenced in the model can be estimated from the experimental data. After a short review on compartmental models, controllability observability and structural identifiability are defined and techniques to check them are provided. The digital computer implementation of the whole procedure is discussed in detail. Some typical program runs regarding the application to biological systems are given.