Detailed histories taken in eighty-one patients suffering from perennial asthma and rhinitis were analysed independently by three trained allergists and their conclusions were compared to the results of three tests: (1) concentration of total serum IgE; (2) skin tests and (3) radioallergosorbent test (RAST). In eleven patients (14%), the three investigators disagreed when estimating the allergic nature of the symptoms. Ten out of forty-four patients (23%), unanimously predicted not to be allergic, had high levels of total serum IgE and skin tests and RAST clearly positive for one or more allergens. The allergists suspected 47% of the allergens detected by skin tests and 55% of those detected by RAST. The case history was the test which most often gave information at odds with that suggested by the other three tests. Our study indicates therefore that a case history not even suggestive of allergy should be complemented by additional tests.