Résumé : Intolerant reactions to acetylsalicylic acid (ASA) and food-additives such as tartrazine (TTZ) and sodium benzoate (BZ) have been described and cross-reactivity has been suggested. However, the topic remains a matter of debate, the more so as the pathogenicity of these reactions is not yet established. The question of cross-reactivity was addressed in our study using in vitro lymphoblastic transformation tests, with incorporation of tritiated thymidine as a marker of activation. As compared with unstimulated control cultures, ASA, TTZ and BZ at 1 or 10 μg/ml concentrations induced in 52.7 percent of the patients a low response (index from 1.5 to 3.5) far from the PHA response (mean index of 10). There was a marked imbalance in favor of cross-reactions to TTZ, ASA and BZ (p < 0.001). Some specificity was suggested since reactivity to these substances could not predict response to any other drug. The clinical relevance of our in-vitro findings remains to be determined but lymphoblastic transformation tests should be considered in the evaluation of intolerant patients.