The stability to heat and cooking of ivermectin was investigated. The drug was insufficiently soluble in water to allow the effect of heating in simple aqueous solutions to be studied. The effect of a range of cooking processes was investigated on pig muscle and liver, cattle muscle and liver and salmon muscle. The drug was found to be stable to the effect of cooking. Some leaching of ivermectin with juices as they exuded from the foods as they were cooked was observed; in one case this amounted to about 50% of the total residue.