Allergies are a widespread phenomenon and one that is in continuous expansion, especially in large cities. A heretofore underestimated allergen, at least in Italy, is the cockroach. Between April and June 2000, we administered a prick test (including the cockroach antigen in the allergen kit) to 163 patients. The prick test was executed utilizing histamine as the positive control and a normal diluent as the negative control; both indoor allergens (including dermatophagoids and dog and cat epithelium) and outdoor allergens (including trees, grasses, pollens and spores) were employed. The results obtained were evaluated by comparing the reaction provoked by these allergens to that of the histamine. About 20% of the patients who reacted to the other indoor allergens also tested positive to the cockroach antigen. Also on the basis of experiences previously carried out in other countries (United States, Korea, Japan, Turkey), the cockroach must be borne in mind as a possible significant cause of allergic reactions in Italy, too.