Seventy-nine aralkyl- and aralkenylamides related to piperamides were synthesized and their nematocidal activity against second-stage larvae of dog roundworm, Toxocara canis, was examined. The activity was greatly dependent on the alkyl chain length and the nature of the amine moiety, but was scarcely affected by the presence or absence of double bond(s) in the chain. The alkyl chain lengths which showed the strongest activity in a series of homologues were m=11 for the pyrrolidine amides and m=13 for the N-methylpiperazine amides. Although piperamides (3, 4-methylenedioxyphenyl homologues) showed the strongest activity among the homologues tested, methoxy substituent(s) on the aromatic ring did not have much effect on the activity. However, conversion of the methoxy group to a hydroxy group greatly decreased the activity and shortened the chain length giving the strongest activity. Calculated log P values of non-phenolic aryl-piperamides fell in the range from 3.5 to 4.5, whereas those of hydroxyphenyl-piperamides were smaller, suggesting that different mechanisms are involved in the nematocidal activity of phenolic and non-phenolic compounds.