The study of the biological tissue varies its behavior, in function of the frequency to which it is subjected. The functions of Cole-Cole, Debye and Lorentz are considered the most used to study the parameters of conductivity and permittivity of biological tissue such as: liver, stomach, gray matter, pancreas, blood, breast tissue to name a few. Depending on the frequency, there may be three different relaxation times. These depend on the nature and physical characteristics of the tissue and its effect in the presence of an electromagnetic signal. The Cole-Cole function is most appropriate when considering a study in the frequency domain, and the Debye function is established to perform the study in the time domain. It is of particular interest to make a comparison between the methods of Cole-Cole and Debye, to define the advantages and disadvantages of each of them. The Lorentz function is used for frequencies of the Tera-Hertz order. Comparative graphs are obtained between both for the biological tissues mentioned above. For each of them the electrical parameters are calculated in a frequency range between 100 Hz and 10 GHz.