The inhibitory effects of two synthesized 3-nitrosalicyl-N-dodecylamide and 2-hydroxy-3-N-dodecylamide-pyridine on the respiratory chain had been compared by using heart muscle preparation from pig heart.3-nitrosalicyl-N-dodecylamide showed stronger effect than 2-hydroxy-3-N-dodecylamide-pyridine on all the three Q-related enzymes of NADH-Q reductase,suceinate-Q reductase and QH₂-cytochrome c reductase.No any inhibitory effect of this two compounds on the terminal oxidase had been observed.The hydroxy groups in the rings of both compounds may be involved in the inhibitory effect through their disturbance on the hydration and dehydration of ubiquinone.