Antinociceptive effect of docosahexaenoic acid was not attenuated by administration of naloxone in mice with CFA-induced arthritis. Mice injected with Complete Freund’s Adjuvant (CFA) were treated daily with 30 mg/kg docosahexaenoic acid (DHA) or with vehicle from day 15 until day 25 after CFA injection. At day 25, 3 mg/kg naloxone (NLX) was administered subcutaneously (s.c.) 90 minutes after DHA administration. Behavioral analysis was performed at 30 minutes after NLX administration. The beneficial effect of DHA on spontaneous pain (A) and horizontal exploratory activity (B) was not significantly affected by NLX. The number of vertical rearings was not significantly affected by NLX (C). i.a. = intraarticular; p.o. = oral. Each bar represents the mean ± SEM. *P < 0.05 vs. i.a. CFA + i.a. vehicle + s.c. vehicle by one-way analysis of variance followed by post hoc Bonferroni correction.