The role played by dipolar interactions in the coercive field and remanence of nanoparticle systems is studied using different concentrations of nearly monodisperse nanoparticles of gamma-Fe2O3. The 9.0 nm particles are isolated by organic encapsulation and diluted in paraffin. Magnetic properties were investigated by means of hysteresis obtained at different temperatures, zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves, and the so-called Delta M technique. The analysis of the experimental data points to the existence of a demagnetizing role played by the dipolar interaction in the coercive field. (C) 2006 American Institute of Physics.