Aim To investigate the effects of leucine-enkepha-line(L-ENK) on the proliferation, the DNA synthesisand c-fos oncogene expression of vascular smooth mus-cle cell (VSMC).Methods Techniques of cell culture, MTTmethod, 3 H-thymidine incorporation and Dot blot.Results L-ENK (10-5 mol/L) could markedly in-hibit the proliferation, DNA synthesis and c-fos onco-gene expression of VSMC. Naloxone (10-6 mol/L),opioid receptor antagonist, had no effect on the prolif-eration, DNA synthesis and c-fos oncogene expressionof VSMC, but, naloxone could antagonized the in-hibitory action of L-ENK to the proliferation ofVSMC. The inhibitory action of L-ENK to the VSMCcould be antagonized by the noradrenaline (10-5mol/L),adrenoceptor activator.Conclusion L-ENK inhibit the proliferation, DNAsynthesis and c-fos oncogene expression of VSMC byactivation of opioid receptors.