The physiological responses of rainbow trout to acutely lethal aqueous concentrations of the suspected polar narcotics phenol, 2,4-dimethylphenol, aniline, 2-chloroaniline and 4-chloroaniline were examined. Visible signs of intoxication included tremors that progressed to whole-organism clonic seizures, followed by general depression and respiratory-cardiovascular collapse. Tremors and seizures were usually initiated with coughs. The most striking changes in the respiratory-cardiovascular parameters for all five toxicants included elevated cough frequency (coincident with seizures), ventilation frequency and hematocrit, and depressed gill oxygen uptake efficiency, arterial pH, total arterial oxygen and total arterial carbon dioxide. The physiological responses noted were attributed to the initial muscular activity associated with seizures followed by respiratory-cardiovascular collapse. Using phenol as a model compound, these effects were found to be reversible when intoxicated fish were exposed to chemical-free water. Principal components analyses of the physiological responses demonstrated that the 11 monitored variables were highly correlated.