Arthral, abdominal and renal symptoms in Henoch-Schönlein purpura (HSP) were scored. Coagulation factor XIII (F XIII) activity was determined in fifty-six children with HSP and the correlation with the severity score of the clinical symptoms was investigated. As a result, it was found that the decrease in F XIII level was correlated with the severity score of clinical symptoms, particularly abdominal symptoms. Based on the results, a controlled study was performed in 24 cases with moderate symptoms divided into a group treated with F XIII concentrate and a non-treated group to investigate clear-cut efficacy as a next study. In three days after the administration the symptoms were improved remarkably in accordance with the increase of F XIII level compared with non-treated group and scoring of clinical symptoms was confirmed to be useful for assessing the application of the F XIII concentrate to HSP.