Paracoccidioides brasiliensis is a thermal dimorphic fungus which in the host environment exhibits a multinucleated and multibudding yeast form. The cellular and molecular mechanisms underlying these phenotypes remain to be clarified, mostly due to the absence of efficient classical genetic and molecular techniques. Here we describe a method for gene expression knockdown in P. brasiliensis by antisense RNA (aRNA) technology taking advantage of an Agrobacterium tumefaciens-mediated transformation (ATMT) system. Together, these techniques represent a reliable toolbox that can be employed for functional genetic analysis of putative virulence factors and morphogenic regulators, aiming to the identification of new potential drug targets.