Three new pyridine alkaloids were detected in the pygidial glands of some Stenus species. The chemotaxonomic significance of the occurrence of these alkaloids and stenusine in different Stenus species is discussed. The antimicrobial properties of (Z)- and (E)-3-(2-methyl-1-butenyl)-pyridine and the deterrent activities of stenusine and norstenusine were investigated.