Thirty‐three adult asthmatic patients suspected of mould allergy were investigated by in vitro and in order to tests in order to establish a specific diagnosis of asthma caused by the mould speciesCladosporium. The patients were evaluated by daily symptom scores in the peakCladosporiumseason, bronchial provocation test (BPT), skin prick test (SPT), RAST, histamine release from basophil granulocytes (HIST), and crossed radio‐immunoelectrophoresis (CRIE), and the results were scored as negative (score 0), equivocal (score 1) or positive (score 2). Based on daily symptom scores and the result of BPT the patients were classified as being manifest allergic (asthma) toCladosporium(positive allergy), inconclusive or negative. Positive allergy was defined as asthma symptoms oscillating with the spore concentration and a BPT score 2 (positive at allergen concentration<10,000 BU). Negative allergy was defined as NO asthma symptoms and a negative BPT (score 0) and inconclusive in the case of symptoms and BPT sum of score 1‐3. According to the classification a final diagnosis (positive or negative) could be established in 85% of the patients. “False positive” tests were found: for BPT in 27%, SPT 18%, RAST 0%, HIST 18%, and CRIE 0%. The corresponding figures for “false negative” were; BPT 0%, SPT 0%, RAST 27%, HIST 18%, and CRIE 23%. The relative risk of being allergic in spite of a negative test result was 0 % for BPT and SPT, and 25‐30 % with RAST, HIST, and CRIE. In the case of positive test the risk was 90‐100%. Excluding BPT, SPT was found to be the optimal single test to predict/rule out clinical allergy. A stepwise combination of positive SPT and positive RAST was found exclusively in patients clinically evaluated as positive, and does not call for an additional BPT. Using a potent allergenic extract a negative SPT excluded clinically important allergy. The primary conclusion of the study, however, is that the final diagnosis ofCladosporiumasthma could not be based on a positive BPT alone (due to “false positive”), but only on a combination of clinical symptoms during the spore seas