The Brugia pahangi infective larval response to jird serum was studied using an agar plate assay. Larvae placed onto the agar remained at the same place for 60 min. Once the larvae were stimulated by serum, more than 95% oriented towards the serum and reached it within few minutes. This larval response was inhibited by an activator of phosphodiesterase (imidazole), adenylate cyclase inhibitors (SQ22536 and MDL-12330A) and protein kinase A inhibitor. An inhibitor of phosphodiesterase (IBMX), an activator of adenylate cyclase (forskolin) and an membrane permeant analogue of cAMP (8-bromo-cAMP), caused a number of larvae to move out from the inoculation area towards the other zones. To our knowledge, this is the first report of a chemotactic response by B. pahangi larvae to host serum. We conclude that B. pahangi larvae show a chemotaxic response to host serum, and that cAMP and cAMP dependent protein kinase are involved in the signal transduction.