Ten novel isocyanocyclohexane compounds that possess an oxygenic functional group at the 4-position were synthesized and evaluated for their antifouling activity against the larvae of the barnacle Balanus amphitrite with the aim of exploring the structure-activity relationships further. The anti-barnacle effect of the synthesized compounds was in the EC50 range of 0.0096-17.0 microg ml(-1). Some ester derivatives exhibited extremely high antifouling activities, and none of the synthesized isocyanocyclohexane compounds showed significant toxicity. The results suggest that the ester function is one of the important groups in the expression of potent antifouling activity in isocyano compounds.