The purpose of this study was to determine if 50 days of resistance training and arachidonic acid (AA) supplementation elicited changes in body composition, performance variables, hormonal/cytokine levels (i.e. prostaglandins, free and total testosterone, cortisol, and interleukin-6) and/or intramuscular markers [i.e. myosin heavy chain (MHC) I, -IIa, -IIx mRNA and protein levels] in resistance-trained males. Thirty-one subjects (22.1±5.0 yrs, 86.1±13.0 kg, 178.9±3.4 cm, 18.1±6.4 % body fat) were randomly assigned to a placebo (P: n=16; 1 g corn oil/day) or AA group (AA: n=15; 1 g AA/day) and were given supplemental protein in order attain an optimal protein intake of 2 g/kg/day while participating in a 2 d/wk upper body and 2 d/wk lower body resistance training regimen. Body composition, bench press one-repetition maximum (1-RM), leg press 1-RM and Wingate bike sprint tests were completed at 0, 25 and 50 days. Fasting blood was taken on days 0, 25, and 50 and muscle biopsies were taken from the vastus lateralis on days 0 and 50. Body composition, performance variables, hormonal levels and MHC mRNA and protein concentrations were analyzed by ANOVA with repeated measures while independent t-tests were used to assess changes in MHC mRNA expression. A significant increase was observed in Wingate relative peak power in the AA group (p=0.015). Statistical trends were found for PGE2 increases (p=0.06) and IL-6 decrements (p=0.07) in the AA group and a significant decrement in percent changes in MHC IIx mRNA expression was present in the AA group (p=0.015). Results suggest that AA supplementation in trained males may exert favorable alterations in training adaptations and fasting prostaglandin and IL-6 levels. However, additional research is needed to examine this hypothesis.