The acid protease Acp1 is produced by Sclerotinia sclerotiorum during plant infection. We explored the mechanism involved in the triggering of that production and found that cyclic AMP played a positive role. Acp1 could be produced in the sole presence of exogenous cyclic AMP. The use of molecules known to increase or decrease the intracellular cyclic AMP levels confirmed the impact of this nucleotide on the protease production and suggested its endogenous site of action. Further pharmacological studies showed the specific effect of cyclic AMP on Acp1 production and suggested that protein kinase A would be its likely target. Together, these results provide the first indication that the production of a pathogenesis-related fungal protease could depend on a cyclic AMP/Protein kinase A signalling pathway.