OBJECTIVE: To study the changes and the role of platelet alpha granule membrane protein (GMP 140) and thrombomodulin (TM) in children with Henoch Schenlein purpura (HSP). METHODS: Plasma concentrations of GMP 140 and TM were assayed using ELISA in 30 children with HSP. The correlation between GMP 140 and TM was studied. Sixteen healthy children served as the controls. RESULTS: The plasma concentrations of GMP-140 and TM increased in the acute phase compared with those in the controls [( 87.35 ± 21.74 ) μg/L vs ( 38.43 ± 19.16 ) μg/L;( 4.53 ± 1.33 ) μg/L vs ( 2.90 ± 0.19 ) μg/L] (both P< 0.01 ); and the plasma GMP 140 concentration returned to the normal level during in the remission phase. The plasma concentrations of GMP 140 and TM in children with HSP complicated by renal lesions were apparently higher than those without renal lesions [( 90.21 ± 22.03 ) μg/L vs ( 63.70 ± 17.44 ) μg/L, P< 0.01 ; ( 4.69 ± 0.22 ) μg/L vs ( 4.01 ± 0.37 ) μg/L, P< 0.05 ]. There was a positive correlation between GMP 140 and TM (r= 0.713 ,P< 0.01 ). CONCLUSIONS: Vascular endothelial damages and platelet activation may be the two important factors in the pathogenesis of HSP. Dynamic measurement of plasma concentrations of GMP 140 and TM is of great value in assessing progress and prognosis and determining proper treatment for HSP.