Vaccines, antibiotics, and other therapeutic agents used to combat disease in poultry generate recurring costs and the potential of residues in poultry products. Enhancing the immune response using alternative approaches such as selection for increased disease resistance or dietary immunomodulation may be effective additions to the portfolio of strategies the industry applies in poultry health management. The objective of this study was to characterize the effects of dietary supplementation with 3 immunomodulators [ascorbic acid, 1,3–1,6 β-glucans from baker's yeast, and corticosterone] on cytokine gene expression in the spleen of 3 distinct genetic lines of chickens. Relative mRNA expression levels were determined using quantitative reverse transcriptase PCR for IL-1β, IL-2, inducible nitric oxide synthase, and toll-like receptors 4 and 15, all of which play important roles in chicken immune function. Expression data were analyzed by mixed model analysis. The only significant effect detected was sex effect (P < 0.04) on expression of IL-1β. The present findings suggest the need for further investigations into the effects of dietary immunomodulators on cytokine gene expression in chickens so as to generate a better understanding of the immunomodulation process.