The 96-h LC50's for potassium permanganate (KMnO4) ranged from 0.750 mg/liter with channel catfish, Ictalurus punctatus, to 3.60 mg/liter with goldfish, Carassius auratus, in laboratory tests. The toxicity of KMnO4to fish is greatest in water of lower temperatures, in harder water, or in higher pH water. KMnO4is effective for detoxifying the fish toxicant antimycin in laboratory waters of pH 6.5 to 9.5. The half-life for antimycin exposed to 1.0 mg/liter of KMnO4ranges from 7 to 11 minutes in the different pH waters at 12 C.