In this work the effects caused by 0.1mM picloram on the white-rot fungi Ganoderma lucidum and Trametes sp. were studied. At this concentration the herbicide caused an increase in the dry mycelial biomasses as well as in the protein and polyssacharide contents, suggesting an auxin-like action. Picloram also caused oxidative stress which was more accentuated in Trametes sp. The latter was indicated by increases in the levels of catalase, superoxide dismutase, reactive oxygen species, and phenolics. Picloram caused an increase in the laccase activity in Trametes sp. (from 93.0±12.0 to 180.0±2 3.0U/g dry biomass), but an unusual reduction in G. lucidum (from 70.2±6.2 to 53.2±8.9U/g dry biomass). Both fungi showed a peculiar mechanism of transitory bioaccumulation of picloram, but none of them was effectively able to degrade the herbicide.