The aim of this study was to evaluate differences of cGMP-PDE activity in salivary glands, between a control group and different benign tumour groups and, where present, with malign tumour groups. Endogen cGMP was evaluated too. The enzymatic reaction used the method of Spoto et al., with minor variations. The samples were organized in six groups: A (Adenolymphoma and Warthins tumour); B (Pleomorphic Adenoma); C (Basaloid Adenoma); D (Myoepitelioma). The control group was represented by healthy patients. In A and B groups, we have analyzed malign pathologies (Adenocarcinoma and Parotid Lymphoma) The benign tumours have more activity than controls, especially in Myoepitelioma (D) but with a decrement in the C group, which presents lower values of cGMP than the other three groups, where the concentration is similar. Between A and B groups, the activity values of malign tumours are similar, higher than controls and than the other benign pathologies, but not higher than in myoepitelioma. The cyclic concentration is similar for malign pathologies, with concentrations lower than controls, similar to Basaloid Adenoma (C).