As an approach to a structure-antischistosomal activity-relationship with possible pharmacological potentiation of the anthelmintic drug praziquantel, a new dipeptide analogue, namely, N alpha-nicotinoyl-L-aspartyl-beta-(1,2,3,6,7,11b-hexahydro-4H-pyrazino[2- 1a]isoquinoline-4-one)-L-phenylalanine methyl ester, was synthesized and antischistosomally investigated in mice infected with S. mansoni cercariae. Parallely, its simple 2-nicotinoyl analogue was synthesized and tested. Both compounds were less, but still, interestingly active (approximately 63 and approximately 66%, respectively) compared to praziquantel (approximately 90%).