Blood coagulation time was determined in five genetically diverse lines of chickens by the capillary tube method. Significant differences were found among lines for coagulation time suggesting genetic influences on this characteristic in chickens. Heritability of blood coagulation as estimated by paternal half-sib correlations was 0.13. The significant difference among lines and the low heritability of this trait indicated that a study of specific coagulation factors was warranted. Prothrombin time, thrombocyte concentration and plasma fibrinogen concentration was investigated in two of the most diverse lines to determine their relative contribution towards variation in coagulation time. Highly significant differences between lines were observed for prothrombin time and concentration of thrombocytes. Differences between lines for concentration of fibrinogen was not significant. The coagulation time and prothrombin time were positively correlated, where as the correlation was negative between coagulation time and thrombocyte concentration and between prothrombin time and thrombocyte concentration, The correlation coefficients between coagulation time and fibrinogen concentration were not significant. The percentage variation in coagulation time attributed to these three coagulation factors was 33 for females and 35 for males, Prothrombin time was the major source of variation in females while the contribution of each of these factors were comparable in males. / M.S.