13 children ranging in age from 1 to 13 years and 1 adult patient had positive patch tests to 2% AlCl3 in water. 13 of them had pruritic excoriated papules, 9 at sites of hyposensitization therapy with aluminium-bound pollen extracts, and 4 at sites of childhood immunization with an aluminium-bound vaccine (Di-Te-Pol). For the 1 adult patient, the positive patch test was not considered to be of current relevance. Aluminium is most likely to sensitize when present in preparations used for immunization.