Flow-through acute toxicity tests on juvenile northern squawfish (Ptychocheilus oregonensis) were conducted with copper, cadmium, and zinc. The 96-hour median lethal concentrations were 18 μg/liter for copper, 1,104 μg/liter for cadmium, and 3,693 μg/liter for zinc in 12 C water. These values, when compared to those for chinook salmon and steelhead parr tested under similar conditions, show that the northern squawfish are more tolerant than the two salmonids to zinc and cadmium but equally sensitive to copper.