Seedling mortality of Alyssum serpyllifolium ssp. lusitanicum and A. murale, both nickel hyperaccumulators, was reduced by increasing concentrations of metal within plant tissues when inoculated with the fungi Pythium mamillatum or P. ultimum, both of which cause damping-off disease of seedlings. Pythium mamillatum, isolated from nickel-rich serpentine soil, was more tolerant of nickel than P. ultimum, isolated from low-metal control soil, and was more pathogenic than P. ultimum towards seedlings containing high concentrations of metal. These results support the hypothesis that metal hyperaccumulation by plants is closely linked to increased protection against disease.