The initial phase of the lipid peroxidation process in leaves of Solanum nigrum var. gigantea, Solanum tuberosum cv Bzura and clone H-8105, which represent non-host resistance, field resistance and susceptibility, respectively, against Phytophthora infestans, was investigated. Based on quantitative and qualitative high-performance liquid chromatography (HPLC) analyses of free and esterified fatty acid hydroperoxides (FAHs), we characterized the lipid peroxidation process induced by the pathogen-derived elicitor, culture filtrate (CF), in leaves of the studied genotypes. In all plants, FAHs generated due to 13-lipoxygenase (LOX) action dominated over those from the non-enzymatic pathway. The FAHs derived from 9-LOX activity were found only in CF-treated leaves of the non-host resistant S. nigrum. However, experiments in vitro and in planta with exogenous linoleic acid (LA) as a substrate for LOX revealed high constitutive activity of 9-LOX in all genotypes, which increased in response to CF treatment. The time course changes in polyunsaturated fatty acid (PUFA) pools in the total lipid fractions as well as the degree of their oxidation suggested that CF-induced PUFA peroxidation was enhanced mostly in S. nigrum, less so in Bzura and least in the susceptible clone H-8105. The obtained results are discussed in light of the overall biochemical cell status of plants in the studied interactions.