Paraoxonases (PON) are proteins which are coded by the three paraoxonase genes located on the chromosome 7. The main role of paraoxonases is protection against oxidative stress. PON1 can also hydrolyze toxic organophosphates. The PON1 paraoxonase and arylesteraze activities, which represent their ability to hydrolyze organophosphate toxins, are modified by different environmental and toxic factors as well as by the PON1 gene polymorphisms. The aim of the study was to evaluate the influence of the selected polymorphisms of the PON1 and PON2 genes and PON1 enzymatic activity on the risk of sporadic amyotrophic lateral sclerosis (ALS), which is a neurodegenerative disease. The genotyping was investigated in 261 patients with ALS and in 715 healthy controls. The PON1 activity due to paraoxon was investigated in 63 ALS patients and 57 controls, and due to phenyl acetate in 62 ALS patients and 57 controls. Genotyping were performed by the PCR and restrictive enzymes digestions and by the real time-PCR method. The PON1 activity due to paraoxon and phenyl acetate was studied spectrofotometrically. The study revealed that the RR genotype of the Q192R polymorphism of the PON1 gene and the genotype with the allele C (CC+CS) of the C311S polymorphism of the PON2 gene were independent risk factors of ALS. The study did not show any difference in PON1 activities due to paraoxon and phenyl ac ; etate between the ALS cases and controls. It was showed that the PON1 activities were not due to disease duration. However, it was shown that the PON1 activities due to both substrates was determined by the L55M and Q192R polymorphisms.