Microdialysis was used for continuous sampling of biogenic amines from the haemolymph of Spodoptera litula (tobacco cutworm). Six different biogenic amines, including norepinephrine, epinephrine, dopamine, octopamine, tyramine, and serotonin in the microdialysates were simultaneously analyzed by HPLC with a coulometric electrochemical detector. In these samples, dopamine and tyramine existed in relatively high concentrations and octopamine could also be detected. We conclude that the “Insect Microdialysis System” can provide a continuous sampling method from the insect haemolymph without physical stress and consequently increase the sensitivity for detection of changes of the haemolymph biogenic amine level.