The sensitivity of juvenile spot, Leiostomus xanthurus, to total residual chlorine (TRC) in flowing sea-water was investigated. Incipient LC50 bioassays, histopathology, avoidance tests and the combined effect of thermal stress and TRC were used to assess sensitivity. Estimated incipient LC50 values were 0.12 mg/l TRC at 10C and 0.06 mg/l TRC at 15C. Histological examination of spot used in the incipient LC50 bioassay at 15C and sacrificed while alive indicated pseudobranch and gill damage occurred in individuals exposed to a measured TRC concentration of 1.57 mg/l. Spot exposed to lower concentrations of TRC, 0.02-0.06 mg/l at 15C and sacrificed alive showed no consistent tissue damage. Simultaneous exposure of spot to thermal stress (5, 10 or 13C above the acclimation temperature of 15C) at measured TRC concentrations of 0.05-0.07 and 0.34-0.52 mg/l demonstrated a significant, (X2 with Yates correction, P < 0.05) increase in sensitivity to TRC with increased temperature and exposure times for some of the groups tested.