In sensitized albino guinea pigs it was not possible to demonstrate therapeutic activity for jewelweed in poison ivy dermatitis after the outward manifestations became apparent. Neither was it possible to exhibit activity in limiting the biologic activity of poison ivy when poison ivy extracts and jewelweed juice were combined in vitro, or on the skin. This was attributable to a lesser degree of sensitivity in guinea pigs than in man and the greater amounts of ivy toxin necessary to elicit dermatitis exceeded the neutralizing powers of even concentrated preparations of jewelweed. In human subjects jewelweed was of no value in treating experimentally established dermatitis. Jewelweed juice or concentrated solutions of jewelweed enzymes were capable of inactivating more dilute poison ivy extracts when mixed in vitro and tested on human subjects under controlled conditions.