Allergy skin testing for immediate hypersensitivity is affected by a number of factors, some under the control of and others not controllable by the operator. Uncontrollable factors include the patient's age, chronobiological variation, and variation in reactivity between different parts of the body. Controllable factors include medications the patient is using, the quality of the allergy extract employed, the distance between test sites, the choice of prick or intradermal technique, and in the case of percutaneous testing, the device that is used. Considering the importance of the information that is generated by skin testing, and the major therapeutic commitments often resulting, more attention should be given to the techniques employed. It is suggested that operator performance can and should be assessed by relatively simple tests.