Noxious substances released from burning cigarettes may cause hypoxia and neurotoxic effects that impede the development of the central nervous system, including brainstem. Our previous studies demonstrated that endogenous hydrogen sulphide (H2S) participate in regulation of respiration (Hu et al. 2008) and play roles in protection of medullary respiratory centres against injury caused by hypoxia (Pan et al. 2010, 2011) in medullary slices of neonatal rats. 3-Mercaptopyruvate sulfurtransferase (3MST) is one of three enzymes found to produce H2S in mammalian. The present study was conducted to investigate whether 3MST exists in the medulla oblongata and its expression can be affected by intrauterine cigarette smoke exposure in the neonatal rats. Sprague-Dawley pregnant rats were randomly divided into 2 groups, control group and cigarette smoke exposure group (n=8 for each). Cigarette smoke exposure rats were exposed to smoke for 60 min (2 cigarettes for 10 min, at an interval of 2 min, repeated 5 times) twice a day (starting at 09:00 and 16:00, respectively) during gds 7-20. The neonatal (P 1) offspring rats were used in the experimental observation. 3MST mRNA and protein expression in the medulla oblongata were analysed by RT-PCR (n=8) and Western blotting (n=8), respectively, and the levels of 3MST expression in the neurons of some medullary nuclei were examined with immunohistochemical technique (n=6). Values are means ± S.E.M., compared with independent-samples t-test. The results of RT-PCR and Western blotting were repeated 2 times, respectively. RT-PCR and Western blotting analyses showed that 3MST mRNA and protein were expressed in the medulla oblogata in the control group and their expression were promoted in the group of intrauterine cigarette exposure of neonatal rats (1.00 ± 0.13 vs 1.51 ± 0.19 for mRNA, P<0.05; 0.20 ± 0.01 vs 0.43 ± 0.07, P<0.05). Immunohistochemical staining indicated that 3MST existed in the neurons of pre-Bötzinger complex, hypoglossal nucleus, ambiguous nucleus, facial nucleus and nucleus tractus solitarius in the control group and the mean optical densities of 3MST-positive neurons in all the nuclei mentioned above except for the nucleus tractus solitarius were significantly increased in the group of cigarette smoke exposure (values not shown, P<0.05). It can be concluded that 3MST exists in the neurons of medullary nuclei of neonatal rats and its expression can be up-regulated by intrauterine cigarette exposure of the animals. These data preliminarily suggest that 3MST-H2S pathway may be involved in response of medullary neurons to injury induced by intrauterine cigarette exposure.