Lipid A1-position carboxylic acid derivatives represented by general formula (I) wherein R<1>, R<2>, R<3> and R<4> represent each formyl or optionally substituted C2-20 alkanoyl; and R<5> represents hydrogen or methyl. These compounds have the effect of activating macrophages and are useful as immunopotentiators or antitumor agents. These compounds have another effect of suppressing macrophage activities and thus are highly useful as antiseptic agents or anti-inflammatory agents too.
