Objective:To investigate the expression and clinical significance of CD34,COLⅠ and CXCR4 in bronchopulmonary dys-plasia(BPD). Methods:Expressions of CD34,COLⅠ and CXCR4 in peripheral blood from 44 premature infants with BPD on the 1st,3rd,5th,7th and 28th d after birth were measured by flow cytometry(FCM) and the expression differences of CD34,COL I,CXCR4 between BPD group and the non- BPD group were compared. Results:On the 1st d after birth,the expression of CXCR4 increased greatly in BPD group compared with that of non-BPD group. With the increase of days after birth,COLⅠlevel peaked on 28th d in BPD group,while CD34 and CXCR4 levels reduced to the lowest. Data of ANOVA for repeated measurement showed that time and the changes in CD34,COL I and CXCR4 levels caused an interactive effect on the occurrence of BPD(F=77.66,P=0.000). ROC curve displayed that area under the curve of COL I was 0.867,higher than those of CD34 and CXCR4. When COL I was 1.3%,the sensitivity was 69.7% and specificity was 86%. There were statistically significances in BPD group among different time points(P=0.000). Conclusion:Circulating fibrocytes with increased level of COLⅠas well as decreased level of CD34 and CXCR4 are closely related with the occurrence of BPD.