The purpose of this work is to illustrate the increasing interest of biosensors and modified electrodes in the field of pharmaceutical potentiometric and voltammetric analysis. Two amino-acids have been determined using enzyme or bacterial membranes immobilized on gas sensing electrodes. The analytical parameters involved in the optimization of the electrode response, but also microbiological factors are discussed for each electrode. Performances of the electrodes and interferences which may occur are presented. Opportunities of using bacteria to produce specific unstable enzymes are pointed out. Neuroleptics have been potentiometrically determined using polymeric modified electrodes specific to drugs containing a piperazine, piperidine or pyrrolidine group. Some new trends in electrode modification have been developed with special emphasis on voltammetric applications. Physical surface modification of carbon paste electrodes by incorporation of an appropriate catalyst (metalloporphyrine derivative) into the electrode substrate has permitted to analyse several pharmaceutical interesting compounds which exhibit poor voltammetric curves at unmodified electrodes. Electrochemical activation of carbon paste electrodes by electrodeposition of platinum microparticles has extended the performances of this type of sensor, with regard to sensitivity, for the investigation of platinum (II) based antitumor complexes. These modification techniques offer benefits for the quantitative analysis of organic compounds but permit also to investigate more deeply the mechanistic side of the interaction electrode - molecule.