Among the absolute calibration methods for activity quantity of radionuclides the most used in the metrology laboratories are: the 4(Pi Beta - Gama) (coincidence counting), defined solid angle counting, sum-peak (or Gama - Gama coincidence) and 4(Pi Gama) method. The 4( Pi Gama) method is appropriate to measure the activity of radionuclides with complex decay scheme and its implementation at Laboratório Nacional de Metrologia das Radiações Ionizantes, commissioned by INMETRO from 1989, will provide to the expansion of the jobs to supply the users by standard radioactive sources.The determination of activity can be made using calibration factor and/or the efficiency curve. For the implantation of this calibration method at LNMRI, after the selection of the detector and the electronic instrumentation, the attainment of the eficiency curve in function of gamma rays energy, standard sources with one or two peaks each were used. The method is based in (Epsilon)T = 1 - Produtórioi (1 - Ti) where EpsilonT is the total efficiency for each radionuclide and EpsilonTi is the efficiency for each gamma transition of this radionuclide. The detector selected was a 8``x 8`` well type NaI(Tl), with well dimensions 6`` deep and 3`` of diameter, from Harshaw The standards sources used are: Am-241, Pb-210, Mn-54, Co-57, Cd-109, Ce-139, Co-60, Na-22, Y-88 and Zn-65. The preliminary results are consistent with the literature.