Introduction of a lead ion in the form of lead nitrate has been found to induce coagulopathy in human blood. A marked toxic action on the normal hemocoagulative mechanism, under a background of lead intoxication, is manifested through an increase of clotting time for lead treated blood. The in vitro study carried out with citrated human blood samples (n=12) utilized celite as a procoagulant in both the control samples and the lead treated blood samples. Various 500 μl samples of blood were treated with varying molar concentrations of lead nitrate. As a substitute for the lead nitrate solution, the control was treated with 0.1% saline solution. It should be noted that at this concentration, saline solution does not alter the coagulation time of blood. Following the incubation of the samples for 10 min. at 37°C, 200 μl of blood was taken from each sample and recalcified by 20 μl of 0.1 M CaCl2 to initiate clotting for measuring the coagulation time. Results thus obtained indicated a direct correlation between Pb(NO3)2 addition and coagulation time for each sample. Furthermore, anticoagulant activity was shown to increase with higher concentrations of Pb(NO3)2.