Objective To observe the change of neuropeptide of the infant patients with post infection cough (PIC) and explore the possible pathogenesis and diagnostic value.Methods Fifty-two cases with PIC in our hospital were selected as PIC group,while thirty infant patients with bronchopneumonia as pneumonia group.Phlegm cells classification and substance P(S P),neurokinin(NKA),neurokinin (NKB),calcitonin gene-related peptide (CGRP) concentration of the patients in both groups were compared.Results Phlegm cells classification of the two groups showed that,compared with the PIC group,the neutrophils,macrophages,and lymphocytes of the infant patients in the pneumonia group were obviously higher (P ＜ 0.05).After anti-infection treatment,the neutrophils,macrophages and lymphocytes of the infant patients in the pneumonia group were obviously lower(P ＜ 0.01).The phlegm cells classification of the PIC group had not changed significantly before and after treatment (P ＞ 0.05).After treatment,the phlegm cells classification of both groups had no significant difference (P ＞ 0.05).During the progress of treatment,there was no evident change for the eosinophils (P ＞ 0.05).Neuropeptide of the two groups showed that,before treatment,the SP and CGRP of the patients in the PIC group were (538.4 ±432.2) ng/L,(123.6 ±70.2) ng/L,and that in the pneumonia group were (613.2 ± 345) ng/L,(156.2 ± 82.6) ng/L.There was no significant difference (P ＞ 0.05).After treatment,the SP and CGRP of the PIC group were (552.8 ± 421.7) ng/L,(133.5 ± 81.3) ng/L,and there was no significant difference (P ＞0.05).While the SP and CGRP of the patients in the pneumonia group were (156.2 ± 131.2) ng/L,(741.2 ± 35.4) ng/L,they were obviously lower (P ＜ 0.01).There was statistical difference compared with the PIC group after treatment (P ＜ 0.01).The NKA and NKB had not changed significantly before and after treatment.Conclusion Airway neurogenic inflammation mediated SP and CGRP plays a key role in the acute and chronic infections.The increase of SP and CGRP is closely related to the morbidity of PIC.So SP and CGRP is a reference index for early detection of PIC.