Polymerase chain reaction and cDNA library screening approaches were employed to identify a putative member of the highly conserved family of ATP-binding cassette transport proteins from Fasciola hepatica. At the predicted protein level, the F. hepatica sequence identified in the present study shares 43% and 36% identity with the Schistosoma mansoni SMDR2 and human MDR1 ATP-binding cassette transport sequences, respectively. Northern blot and reverse transcriptase-PCR analyses have demonstrated that expression of the F. hepatica ABC-transporter homologue is confined to immature parasites. The biochemical basis for the stage-specific expression of the ATP-binding cassette transporter homologue within F. hepatica remains to be determined.