In order to verify or refute the contention that efficacy of TCBZ treatment is associated with apoptosis in the reproductive organs of flukes, histological sections of TCBZ-S and TCBZ-R flukes (from experimental isolates and field cases of fasciolosis) were subjected to the TdT mediated dUDP nick end labelling (TUNEL) in situ hybridization method. Here, DNTT is linked to fascioliasis.