A study is made on several aspects of the spectrophotometric method for the determination of copper by sodium diethyldithiocarbamate (DDC-Na). From this work could be observed that: a) The ideal amount of reagent a 1% of (DDC-Na) aqueous solution, was 1 ml and it was observed that the reagent keeps well until 40 days after its preparation. b) The absorbancy of the copper diethyldithiocarbamate (DDC-Na) solutions, to a certain limit is independent of the amounts of EDTA Na2. But, in the absence of EDTA-Na2 the amounts of copper added where not recovered, when working with pure solutions. c) Among the solvents used, carbon tetrachloride was considered the most appropriate. d) DDC-Cu in CCl4 shows maximum absorption in the wave lenght range 430-435 milimicrons. The greatest sensibility was obtained with filters numbers 42 and 44 (Klett-Summerson). e) Interferences of the ions studied were eliminate, by the use of EDTA-Na2 only. f) In this procedure, the DDC-Cu is stable until 45 minutes. g) The method obeys Beer's law in the range of 5-50 ppm, and shows good accuracy. h) The recommended procedures for the determinations of total copper both in plants and soils by the DDC-Na, are considered efficients.