Spinel Fe3O4 nanoparticles have been produced through ball milling in methyl-alcohol (CH3OH) with the aim of producing samples with similar average particle sizes (d) and different interparticle interactions. Three samples with the Fe3O4 to CH3(OH) mass ratios R of 3, 10 and 50 wt% were milled for several hours until particle size reached a steady value ( similar to6-10 nm). A detailed study of static and dynamic magnetic properties has been undertaken by measuring magnetization, ac susceptibility and Mossbauer data. As expected for small particles, the Verwey transition was not observed, but instead superparamagnetic (SPM) behavior was found with transition to a blocked state at T-B similar to 10-20 K. For samples having 3 wt% of magnetic particles, dynamic ac susceptibility measurements show a thermally activated Arrhenius dependence of the blocking temperature with applied frequency. This behavior is found to change as interparticle interactions begin to rule the dynamics of the system, yielding a spin-glass-like state at low temperatures for R = 50 wt% sample. (C) 2004 Kluwer Academic Publishers.