Enchytraeids are small soil annelids who have been frequently and successfully used as testing organisms to determine possible hazards of chemicals entering the soil or to evaluate contaminated soil quality. Standardized tests for Enchytraeus sp. target only mortality and reproduction as measurable endpoints. However, no-effect on survival and reproduction doesnt mean healthy animals. Oxidative stress caused by toxic substances or other environmental factors is one of the main toxicity mechanisms. Biochemical or cell processes alteration related to oxidative stress can serve as an early indication of more pronounced effects. Biochemical markers of oxidative stress and detoxification have never been investigated in enchytraeids, although their potential as sensitive parameters of chemical exposure might be expected. To enable use of these parametres in future studies with enchytraeids, baseline levels and variability have to be described first. In our study, glutathione - GSH, glutathione-S-transferase - GST, glutathione peroxidase - GPx, glutathione reductase - GR, and lipid perxidation - LP were measured in Enchytraeus crypticus samples from the age synchronized and non-synchronized populations cultured on agar or in the artificial soil. Dependence on sample size, and culture medium, as well as variability range and its sources were investigated.