The objective of the study was to evaluate thein vitroeffect of aqueous suspensions of commercial multi-walled carbon nanotubes (MWCNTs) on spores of three entomopathogenic fungus species ofBeauveria bassiana. Spores were placed in contact with MWCNTs for 1, 24, 72 and 216 h and then anin vitroevaluation in the subculture was performed on the linear growth of the vegetative mycelium of the spores after the contact with nanomaterial, as well as its sporulation after completion of the culture. No fungistatic effect of MWCNTs againstB. bassianaspores was identified. Modification of vegetative mycelium surface growth in the culture of spores after contact with MWCNTs was mainly due to less effective inoculation, especially when shorter contact times with nanomaterial were applied. For one of the investigated strains, growth stimulation was observed in the culture of spores in contact with nanotubes for 72 and 216 h. Based on the significant intensification of sporulation observed in combination with the longest (216 h) contact with the investigated spore strains before culture with MWCNTs, it can be concluded that the tested nanomaterial constitutes a stress factor and may modify the metabolism ofB. bassianacells. Detailed evaluation ofB. bassianametabolic changes induced by MWCNTs should be conducted. [ABSTRACT FROM PUBLISHER]