Thrombotest (TT) values were studied in patients fed an ordinary diet and on continuous and well controlled warfarin therapy because of deep venous thrombosis or pulmonary embolism. The aim was to characterize the effect of single and multiple administrations (daily during one week) of vitamin K1 (Konakion), vitamin K-rich vegetables such as spinach and broccoli, and table wine. Single administration of 250 micrograms vitamin K1, 250 g spinach, 250 g broccoli and 37.5 cl wine did not result in TT-values outside the therapeutic range. However, when Konakion, broccoli and spinach were given daily during one week the TT-values tended to rise above the therapeutic limit, requiring dose adjustment. On the basis of this study it appears that excessive intake of vitamin K-rich food and a moderate intake of alcohol on one occasion may be permitted during anticoagulant therapy.