In this work we present an investigation on the behavior of microsomes containing human cytochrome P450 in cyclic voltammetry for drug detection. The microsomes are adsorbed on the surface of multi-walled carbon nanotubes by drop-casting. We demonstrate that the hydrophobic and highly electroactive surface of multi-walled carbon nanotubes enables to distinguish more clearly the contributions in reduction peak current attributed to the enzymatic components of microsomes. Voltammetric measurements were performed under several experimental conditions with two cytochrome P450-isoforms, 1A2 and 3A4. We show that the reduction current for the component of cytochrome P450-microsome linearly increases in the presence of a substrate.