As compared with hemostatic therapies alone, FXIII cotreatment increases whole blood clot weight. Hemophilic whole blood was treated with protein buffer (0.75% w/v bovine serum albumin in 0.9% sodium chloride solution), FXIII (2 IU mL−1) or (A) recombinant activated FVII (rFVIIa) (25 nM), (B) plasma-derived anti-inhibitor coagulant complex (FEIBA) (1 IU mL−1), or (C) recombinant B-domain-deleted porcine FVIII (rpFVIII) (1 IU mL−1), with or without FXIII, and clotted with tissue factor and recalcification. Contracted clots were weighed. Dashed lines indicate ranges of clot weights for n = 4 non-hemophilic donors. Bars show the mean ± standard error of them mean for n = 5–8 individual hemophilic donors per treatment. Treatments were compared by the use of repeated measures ANOVA with the Holm–Sidak multiple comparisons test.