Three Solanum genotypes with various polygenic resistance levels to the oomycete pathogen Phytophthora infestans (Mont.) De Bary were studied for their antioxidant response to the pathogen culture filtrate (CF). Detached plant leaves were treated with CF for 6, 18 and 30 h, and assayed for changes in hydrogen peroxide content, total ascorbate and glutathione pools and redox ratios (reduced form to total pool), as well as for changes in activities of ascorbate peroxidase, glutathione reductase and glutathione-S-transferase. In CF treated leaves of non-host resistant S. nigrum var. gigantea and field resistant S. tuberosum cv Bzura, the H(2)O(2) content did not change in comparison to water treated control leaves, whereas in the susceptible S. tuberosum clone H-8105 it decreased below the control level. In CF treated leaves of all genotypes, the total ascorbate pools were relatively unaltered and their redox ratio changed only transiently. In Bzura leaves the total glutathione content increased earlier than in the two other genotypes. The glutathione redox ratio remained rather stable, except for the susceptible clone H-8105, where it decreased transiently by about 42%. The relative increases in activity of all the studied enzymes were the highest in the susceptible clone H-8105. The results are discussed in the light of oxidative processes occurring in CF treated leaves. We conclude that stringent control of pro- and anti-oxidant reactions bringing the H(2)O(2) and/or cellular redox state to the threshold level is decisive for deployment of an effective defense strategy.