Aspirin (ASA) and other non-steroidal anti-inflammatory drugs, which are cyclooxygenase (COX) inhibitors, precipitate asthmatic attacks in ASA-intolerant patients, while sodium salicylate, hardly active on COX by itself, is well tolerated by these patients. However, salicylate moiety appears to interfere with aspirin inhibitory action on platelets and vascular COX. Such interaction, if present at the level of respiratory tract, may be of interest to pathogenesis of ASA-induced asthma. We performed a double-blind, placebo-controlled, randomized cross-over study on the effect of choline magnesium trisalicylate (CMT, trilisate) pre-treatment on ASA-induced adverse reactions in nine patients. Pulmonary function tests, nasal symptoms score, PNIF and serum salicylate levels were monitored following challenges with threshold doses of ASA. Trilisate administered at a dose of 3000 mg daily for 3 days, offered a moderate protection against ASA-induced symptoms; it diminished the severity and/or delayed the appearance of FEV1 fall. Maximal decreases in FEV1 as well as reaction intensity indexes were significantly lower (P less than 0.02 and P less than 0.002, respectively) after trilisate pre-treatment as compared to placebo. Trilisate also attenuated nasal symptoms in three out of five patients. Although the precise mechanism of the protective action of trilisate is unknown, our data support the possibility of interaction between salicylate and ASA on cyclo-oxygenase locus in the respiratory tract in ASA-intolerant patients.