Pustular patch test reactions to 5% nickel sulfate were regularly produced in patients with atopic dermatitis when patches were placed over areas of skin with (a) follicular papules, (b) erythema, (c) lichenification, and (d) minimal trauma. The pustular patch test reactions seldom occurred in the normal-appearing skin of these patients. However, if the skin was traumatized prior to the patch test, the reaction was produced in the normal-appearing skin of atopic as well as control individuals. No pustular reactions occurred in the follicular lesions of keratosis pilaris, supporting the view that follicular lesions of atopic dermatitis differ from keratosis pilaris. It is suggested that pustular patch test reactions are caused by primary irritation.