This paper examines the application of higher harmonic Non-Linear Electrochemical Impedance Spectroscopy (NLEIS) to characterization of colloidal suspensions of clinically relevant microparticle biomarkers derived from monocytes (white blood cells). This study expands on previous linear EIS investigations of microparticle biomarkers' suspensions and NLEIS studies of non-aqueous colloidal systems. Numerical minimization analysis allowed to develop a more accurate equivalent circuit model for the low frequency region (<1 kHz) and provided qualitative insight into the kinetic and physiological parameters of the system. The developed NLEIS characterization method permitted to resolve several remaining ambiguities in interpretation of low-frequency linear impedance experimental results for microparticles' suspensions. These results support continued development of the NLEIS method validation and instrumentation for microparticle biomarkers' analysis, further expanding its clinical diagnostic capabilities. (C) 2011 Elsevier Ltd. All rights reserved.