A quantitative real-time reverse transcription polymerase chain reaction (RT-PCR) assay was developed to measure transforming growth factor-β (TGF-β) in Atlantic menhaden (Brevoortia tyrannus), an estuarine-dependent species plagued by ulcerative skin lesions in the estuaries along the eastern United States. Atlantic menhaden were acclimated in a closed system for two weeks prior to initiation of the study. The synthetic glucocorticoid, triamcinolone acetonide (10 mg/kg body weight) was administered by intracoelomic injection and its effect on the splenic mononuclear cell TGF-β mRNA transcription, liver-somatic index, spleno-somatic index, hematology, and plasma chemistry were compared to untreated fish at 48 and 96 h post-treatment. Triamcinolone-treated Atlantic menhaden showed suppression of TGF-β mRNA production, neutrophilia, monocytosis, lymphopenia, and an increase in blood glucose concentrations. The health indices used in this study may help us interpret some of the changes observed during the development of ulcerative skin lesions in wild-caught menhaden.