The membrane-proximal external region (MPER) of gp41 is considered as a prime target for the induction of neutralizing antibodies, since it contains the epitopes for three broadly neutralizing antibodies (2F5, 4E10 and Z13). Here we present a novel gp41 construct (HA-gp41) comprising gp41 HR2 and MPER fused to two triple-stranded coiled-coil domains at both ends. HA-gp41 is trimeric, has a high helical content in solution and forms rod-like structures as revealed by negative staining electron microscopy. Immunization of rabbits with HA-gp41 induced antibodies directed against MPER, which failed to exert significant neutralization capacity against envelopes from primary isolates. Thus trimerisation of MPER regions does not suffice to induce a potent neutralizing antibody response specific for conserved regions within gp41.