AbstractWe studied the kinetics of C1‐inhibitor (C1‐INH) and other complement parameters in a self‐limited edematous attack (EA) in a patient with hereditary angioedema due to C1‐INH deficiency to better understand the pathomechanism of the evolution, course, and complete resolution of EAs. C1‐INH concentration and functional activity (C1‐INH_c+f), C1(q,r,s), C3, C4, C3a, C4a, C5a, and SC5b‐9 levels were measured in blood samples obtained during the 96‐hour observation period. The highest C1‐INH_c+f, C4, and C1(q,r,s) levels were measured at baseline, and their continuous decrease was observed during the entire observation period. C4 depletion started at prodromal phase, and C4 was lowest after the maximum severity peak. Compared to baseline, C4a level was four times higher 7 hours before the onset of the attack. C1‐INH did not increase after resolution of the attack suggesting that factors other than C1‐INH may be important in this process. C4a may be a useful biomarker for the prediction of EAs.