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Abstract: In this study the effects of exposure to two air temperatures (15 and 27.5°C) and three graders commonly used in South Australia (Rotary, Flat Bed and Inside/Out) on Pacific oysters were investigated using post-exposure or post-grading catecholamine levels as a stress indicator. During the 48h experimental period the circulating dopamine and noradrenaline levels of oysters exposed to 15°C air temperature did not differ significantly from controls sampled directly from the 15°C water tank. Conversely, in oysters exposed to 27.5°C air temperature, dopamine and noradrenaline became significantly different from controls after 8 and 12h air exposure, respectively, and then returned to the control levels at 24h. Significant increases (P <0.05) in circulating noradrenaline and dopamine levels were observed in oysters graded by the Flat Bed and the Inside/Out graders. The circulating noradrenaline concentrations in oysters subjected to the Flat Bed grader were significantly higher (P <0.05) than those observed in the Rotary graded oysters and close to being significantly higher (P =0.052) than those levels measured in the Inside/Out graded oysters. The circulating noradrenaline levels in oysters subjected to the Inside/Out grader were, in turn, significantly higher than those recorded in the Rotary graded oysters. These results suggest that in relation to the three graders used in South Australia, the Flat Bed induces the highest stress levels in oysters and the Rotary grader the lowest. [Copyright &y& Elsevier]