Fusion protein of single-chain Fv-tuftsin (scFv-tuftsin) was constructed and expressed in yeast Pichia pastoris expression system. Immunisation of mice with scFv-tuftsin fusion protein enhanced the humoral immune responses, including anti-idiotypic (Ab2) and anti-anti-idiotypic (Ab3) inductions, when compared to scFv alone as a control. In marked contrast to response pattern in Ab2 induction, there was only a transient induction of Ab3 at day 14 of post-immunisation.