Infectious pancreatic necrosis (IPN) virus has been found in brook trout in two northern Ontario salmonid hatcheries. A study indicated that the disease in Ontario did not present the "explosive" and severe mortalities among salmonid fry that one might expect from published reports. Infectivity experiments were carried out at 40, 50 and 60°F to determine the contribution of water temperatures to levels of IPN-associated mortality. At 5°F, a high mortality occurred in brook fry. This was decreased at 6°F and absent at 40°F. Other factors contributing to a low mortality are discussed.