The eventual difficulties of diagnosing professional asthma sometimes need the help of methods of complementary diagnosis. The histamine-release test and that of basophils granules liberation are studied in this work, concerning 12 substances with a suspected allergenic action (saw-dust, textile fibres, chemicals, products of plant origin). The histamine-release and granules liberation tests were performed according to the techniques described respectively by Lichtenstein and Benveniste. Both examinations were positive in a concording manner in 8 cases out of 12, but this positivity was difficult to interprete for etiopathogenic reasons. The study of the curve of histamine-release in relation with the dose of allergen used in the test nevertheless enables to differentiate two types of answers, one related to an allergic mechanism, the other to an irritative one. These observations led to the deduction that a positive granules liberation test could be due to a non allergic mechanism. Negativity in both tests does not allow the rejection of the part played by these substances into the genesis of respiratory signs. Indeed these tests only investigate one part of the mechanisms which can be involved: direct stimulation of vagal irritant receptors and the plain pharmacological reactions escape from this type of biological investigations. The biological tests studied in this work can be used in a complementary fashion in the etiological survey of professional asthma but they cannot replace the realistic tests, more reliable because they react whatever the etiopathogenic mechanism involved.