Allergy to flour was studied by many autbors (2, 3, 4, 7, 9, 16, 29, I,!,, 35, 39, etc.). However, few investigators used cballenge tests as a diagnostic tool (20,23,35,36). To us, challenge tests appeared particularly indicated in studying the allergy to flour since. 1) Many if not most allergic bakers display concomitant positive skin tests to various allergens (4, 5, 9, 16, 20, 29, •},2, 40) ; in these subjects a careful anamnesis could occasionally distinguish between latent and manifest allergy. For instance, in bakers with paroxysmal dyspnea occurring only at the working place, a concomitant positive skin test to bouse dust expresses only a latent allergy; but in bakers with asthma attacks both at work and at home (even during holidays or leaves), allergic etiology may be diflicult to assess. 2) Anamnesis and skin tests are not sufficient wben studying the part played in flour allergy by its contaminants (arthropodes, fungi, bacteria). 3) In occupational respiratory allergy, challenge tests reproducing the spontaneous complaints are tbe most convincing diagnostic procedures (30, 31)-Modern equipment diminisbcd considerably the incidence of allergy to flour (33), utilization of persulfate (41) was