The development of production processes that can reduce the environmental impact, offer waste reduction and increase energy efficiency is an important step in the field of application of nanotechnology. In this work the filamentous fungus Neurospora crassa was screened and found to be successful for the production of mono and bimetallic Au/Ag nanoparticles (NPs). Analysis by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM) confirmed the biosynthesis of NPs by the fungus. The shape of NPs was found to be mainly spherical with average diameter of 11nm for silver and 32nm for gold, when the fungus was exposed to the aqueous solutions of 10(-3)M of AgNO(3) and HAuCl(4), respectively. EDS analysis also confirmed the formation of alloy-type Au/Ag bimetallic NPs when three different ratios of AgNO(3)/HAuCl(4) were used. TEM images of thin sections of N. crassa cells confirmed the intracellular formation of silver and gold NPs. The results obtained indicate that N. crassa can be a potential "nanofactory" for the synthesis of metallic NPs. The use of this organism will offer several advantages since it is considered as a non-pathogenic organism, has a fast growth rate, rapid capacity of metallic ions reduction, NPs stabilization and facile and economical biomass handling. 2010 Elsevier B.V. All rights reserved.