Technical Abstract: Juvenile channel catfish (Ictalurus punctatus) were exposed to copper sulfate in a simulated therapeutic treatment episode and changes in physiological stress indicators were monitored during and after the exposure episode. Plasma cortisol concentrations rose throughtout the 24 hour copper sxposure episode and declined when the exposure was discontinued. Plasma glucose concentrations were elevated immediately upon exposure and rose throughout the 24 hour exposure. The peak of glucose concentration was folllowed by a slow decline to the pre-exposure concentration by 78 hours of the study. Plasma lactate concentratios did not change until after exposure was discontinued at 24 hours. Thirty hours after exposure was discontinued, there was a significant increase in plasma lactate. Plasma chlorides were significantly reduced during the course of the 24 hour exposure and remained depressed until 78 hours of the study. No changes were observed in hematocrit values, or in plasma associated aspartate amino trensferase, alanine amino transferase, and lactic dehydrogenase, suggesting that little cellular damage accompanied the simulated treatment episode.