One-hundred and forty asthmatics were tested perorally with acetylsalicylic acid (ASA), and/or with the azo-colour tartrazine; a fall in PEF of more than 20% was accepted as a positive result. About one quarter of the patients displayed a positive reaction to one of the two tested agents. No significant correlation was found between the reactions of these, and the presence of atopy, nasal polyposis, sinusitis, rhinitis, sensitivity to cold air, the age at onset, duration of asthma, or history of sensitivity to alcoholic drinks. The history suggested sensitivity to ingested, possibly coloured, food and drink, in only about one third of the tartrazine-positive cases. The ASA provocation tests were mainly applied to patients with doubtful or negative histories of sensitivity to ASA-containing drugs. The frequency of cross-reactivity between the two tested agents was statistically significant; patients reacting to tartrazine were for the most part, also sensitive to ASA. Tests for sensitivity to analgesics and food additives should be conducted as a routine measure in asthmatics, and sensitive patients should be given information on suitable medication and dietary control.