M.Tech. (Homoeopathy) / The medicinal plant, Arnica montana, in homoeopathic dilution, is commonly used in the treatment of extravasion of blood or bruising (Jouanny, 1984). However, the exact action of Arnica montana on hemostasis, the process of autoregulation by which the body ensures the integrity ofthe vascular system, is still unknown. Arnica Montana contains coumarin, a substance known to have an anticoagulant action. Thus it was thought that Arnica montana 30CH would have an effect on blood coagulation, one aspect of hemostasis.t!he purpose of this study is to determine the effect of the homeopathic remedy Arnica montana 30CH on blood coagulation in vitro. Venous blood was drawn from twenty subjects on two consecutive days and blood coagulation screening tests (namely prothrombin time, thrombin time, activated partial prothrombin time and fibrinogen assay) were carried out on the separated blood plasma. Results from the control (unmedicated plasma), plasma medicated with 20% alcohol and plasma medicated with Arnica montana 30CH were compared. Although the results from this study showed that the homoeopathic medication Arnica montana 30CH had no significant effect on blood coagulation, Arnica montana 30CH may still play a vital role in the process of autoregulation by influencing vascular integrity and platelet activity. Further in-depth studies on these parameters may be warranted. Due to the nature of the data, and on recommendation of the statistician, the results of this study were analyzed in conjunction with two similar studies. These studies looked at the effect of Arnica montana mother tincture and Arnica montana 12CH on blood coagulation respectively. The results of all three studies were statistically analyzed together in order to obtain a more accurate estimate of the within, between and residual variances.