Laboratory tests indicate that methylated spirits, widely espoused as a first-aid treatment for jellyfish stings, causes massive discharge of nematocysts in living tentacles of the box-jellyfish, Chironex fleckeri. This action, together with demonstrated hazards of flammability and intoxication, casts doubt on this substance as a treatment for Chironex stings. In an attempt to find a substitute which will be effective in inactivating unfired nematocysts in the tentacles adhering to sting victims, a number of substances were tested in the laboratory. Weak solutions of acetic acid, as well as commerical vinegar, were found to inactivate the penetrating nematocysts of Chironex rapidly and completely. Most other substances tested proved less effective, and some actually stimulated the firing of nematocysts.