Objective To investigate the changes of plasma cortisol and adrenocorticotrophic hormone(ACTH)levels in prema-ture neonates with the infectious diseases.Methods Ninety premature neonates in the neonatal department of our hospital were di-vided into the control group(30 cases),mild infection group(30 cases)and severe infection group(30 cases).The radioimmunoassay was adopted to detect the serum cortisol and ACTH levels on 1,3,7 d after birth in all subjects and the corresponding comparison was conducted.Results The cortisol levels on 1,3,7 d in the mild infection group were (193.04 ±39.48),(151.12 ±35.62 ), (128.37±27.47)ng/mL respectively,the level on 1 d was higher than that on 3,7 d (P <0.05),and the 3 d was higher than that on 7 d (P <0.05).The cortisol level on 1,3,7 d in the severe infection group were (99.43±50.17),(96.52 ±44.69),(131.13 ± 42.73)ng/mL respectively,and the level on 1,3 d was significantly lower than that on 7 d (P <0.05).Conclusion The relative ad-renocortical insufficiency exists in premature neonates with the early stage of severe infection and is manifested by the decline of plasma cortisol level,which could recover to the normal level on 7 d,but the plasma ACTH level has no relation with infection.