In herbivorous insects the Malpighian tubules (MTs) perform the role of eliminating ingested plant-produced metabolites (PPM) from the hemolymph to avoid potentially toxic effects. The basolateral uptake of salicylate, a typical PPM, by the MTs was studied in D. melanogaster using a radioisotope tracer technique. The uptake of [¹⁴C]-salicylate by MTs was shown to be active, saturable and Na⁺-dependant, indicative of carrier mediated transport. The mechanism was inhibited by the general organic anion transport inhibitor, probenecid; the monocarboxylate transport inhibitor, α-cyano-4-hydroxycinnamic acid; several sulphonate compounds; and by ring structure monocarboxylic acids. However, short chain monocarboxylic acids did not show inhibitory effects. In contrast to vertebrate renal tissues, α-keto acids neither trans-stimulated nor cis-inhibited [¹⁴C]-salicylate uptake.