The production of reactive oxygen species (ROS) in cells is well balanced with their elimination by the antioxidant defence system. This balance is essential for maintenance of physiological conditions, and its disturbance (oxidative stress) has been suggested as a potential pathogenic mechanism in a variety of diseases, accompanied by inflammation. In this study, the in-vivo effects of nociceptin (N/OFQ(1–13)NH2) and its structure analogue [Orn9]N/OFQ(1–13)NH2 were studied on markers of oxidative stress in erythrocytes and liver of rats 4 hours after subplantar administration of carrageenan (CG) (1%, 100 µl) in the right hind paw. A considerable inflammatory oedema of the paw was observed. CG did not change blood haemoglobin content, hematocrit value, glutathione level and antioxidant enzyme activities in the erythrocytes, but there was an increase in lipid peroxidation. In liver, CG-induced imbalance was manifested by an increase in lipid peroxidation and a decrease in glutathione level. Both peptides (20 µg, i.p.), when administered alone, had no effect on all parameters tested. When either [Orn9]N/OFQ(1–13)NH2 or N/OFQ(1–13)NH2 was injected simultaneously with CG or 15 minutes before it, they did not affect the CG-induced changes in the antioxidant status of the erythrocytes and liver. Our results suggest that the peptides tested did not play a role in the free radical processes that accompany CG-induced paw inflammation.