Abstract: Agricultural pesticides that are known endocrine disrupting chemicals (EDCs) have been detected in waters in the Great Barrier Reef (GBR) catchment and lagoon. Altered transcription levels of liver vitellogenin (vtg) have been documented in wild populations of 2 GBR fisheries species, and were strongly associated with pesticide-containing run-off from sugarcane plantations. Here, we examine endocrine and physiological biomarkers in juvenile barramundi (Lates calcarifer) exposed to environmentally relevant concentrations of commercial herbicide (ATRADEX® WG Herbicide, DIUREX® WG Herbicide) and surfactant (ACTIVATOR® 90) formulations commonly used on sugarcane in the GBR catchment. Estrogenic biomarkers (viz. liver vtg mRNA and plasma 17β-estradiol) increased following exposure to commercial mixtures but not to the analytical grade chemical, suggesting an estrogenic response to the additives. In contrast, brain aromatase (cyp19a1b) transcription levels, plasma testosterone and 11-ketotestosterone concentrations and gill ventilation rates were not affected by any of the experimental exposures. These findings support the assertion that exposure to pesticide-containing run-off from sugarcane plantations is a potential causative agent of altered liver vtg transcription levels in wild barramundi. Whether exposure patterns in the GBR catchment and lagoon are sufficient to impair fish sexual and reproductive development, and ultimately influence fish population dynamics remains to be determined. Our findings highlight the need to consider both active and so-called inert ingredients in commercial formulations for environmental risk assessments. [Frederieke J. Kroon, Sharon E. Hook, Suzanne Metcalfe & Dean Jones (2015). Altered levels of endocrine biomarkers in juvenile barramundi, Lates calcarifer (Bloch), following exposure to commercial herbicide and surfactant formulations. Environmental Toxicology and Chemistry, online 9th April] Comment