Objective: this study aimed to evaluate in vitro , by means of modified direct contact test, the influence of the organic load of the blood serum on the antimicrobial activity of three endododontic sealers ( Sealapex, Pulp Canal Sealer EWT and AH 26 ). Methods: the ATCC bacterial strains (Enterococcus faecalis, Prevotella intermedia, Prevotella nigrescens, Porphyromonas gingivalis and Fusobacterium nucleatum) where cultivated, washed and re-suspended so as to obtain a suspention that permitted the inoculation of approximately 70 UFC in each well of a plate for cell culture (96 wells). In each well, 10 mg of each sealer were exposed to 100m L of fetal calf serum, washed with PBS and the bacterium inoculum was disposed. An appropriate culture medium was inserted in each well and the plates incubated at 37°C in an appropriate atmosphere. The results were evaluated by visual observation through a stereoscopic microscope. From the wells in which no presence of bacterial strains colonies were detected, aliquots were collected and transferred to another medium and incubated. The turbidity of the medium indicated bacteria growth, characterizing a bacteriostatic effect. Results: Ah 26 and PCS EWT showed bacteriostatic effect when in contact with P. intermedia and P. gingivalis. Only Sealapex demonstrated a modified antimicrobial activity by blood calf serum contact. Conclusions: the organic load of blood serum did not interfere with the antimicrobial activity of these sealers.