This study was designed to investigate the ability of long-term primary cultures of adult human hepatocytes to secrete the main haemostasis proteins. Factors II, V, VII, VIII, PIVKA-II (protein induced by vitamin K 1 absence or antagonist II), fibrinogen and antithrombin were quantified in culture medium by immunological methods and by measuring the coagulant activity of factors II, V and VII. All the haemostasis protein antigens except the factor VIII antigen (FVIII:Ag) were found in the culture medium throughout the culture period. The clotting activity of each factor correlated well with antigen level. In addition, fibrinogen and fibrin were detected in the fibrillar material following incubation of the culture medium with thromboplastin. Moreover, adding vitamin K 1 to the culture medium resulted in a significant increase of factors II and VII and a reciprocal decrease of the PIVKA-II, and adding von Willebrand factor resulted in a drastic increase of the level of FVIII:Ag. We conclude that, in our culture system, normal adult human hepatocytes retain their capacity to secrete haemostasis proteins for at least 30 days.