Summary. Background: Factor XIII (FXIII) is a transglutaminase that cross-links fibrin and other proteins to improve clot strength and resistance to fibrinolysis. Both congenital and acquired FXIII deficiency may result in a bleeding diathesis, and plasma-derived FXIII has been used to treat many of these clinical conditions. Objectives: A clinical study was designed and performed to evaluate the safety, pharmacokinetics, and immunogenicity of recombinant FXIII (rFXIII) administration to healthy adult volunteers. Patients and method: Fifty healthy adult volunteers were enrolled in this randomized, double-blinded, placebo-controlled study. A single dose of rFXIII, ranging from 2 U kg−1 to 50 U kg−1, or placebo was administered. Safety was evaluated by capturing adverse events, clinical safety laboratory studies, and clinical score for deep venous thrombosis. Blood samples were taken for pharmacokinetic and immunogenicity analysis throughout the 28-day follow-up period. Results: Recombinant FXIII was well tolerated, with no serious adverse events or dose-related toxicities. Following a single i.v. injection of 50 U kg−1 rFXIII, the estimated terminal half-life was 270–320 h, the volume of distribution ranged from 40 to 75 mL kg−1, and FXIII activity increased 1.77% per 1 U kg−1 rFXIII administered. Increase in circulating A2B2 and decrease in free FXIII-B subunit indicate in vivo formation of FXIII heterotetramer. An immunogenic response to rFXIII or yeast, the production host, was not observed. Conclusions: Recombinant FXIII was well tolerated at doses of up to 50 U kg−1 in healthy adult volunteers. The safety, pharmacological and immunological profile of rFXIII suggests it should be studied in patients with congenital FXIII deficiency as well as evaluated as a systemic hemostat in patients with acquired FXIII deficiency or hemorrhage.