We have studied the allergen-specific in vitro histamine release (HR) in 38 flour-sensitive bakers and in 10 controls without occupational exposure after whole blood incubation with native wheat and rye flour and compared the results with the findings in RAST, skin and bronchial provocation tests. The mean in vitro HR from whole blood after incubation with rye flour amounted to 38.1% (range 0–100%) in flour-sensitive bakers and to 8.2% in the controls (p < 0.005). Concerning the quantity of HR, no significant differences were found when bakers with meal rhinitis or those with flour-induced asthma were compared. Qualitative analysis, however, showed a close correlation between the frequency of positive HR and the severity of the allergic disorder (rhinitis versus asthma). Comparison of in vitro HR with the findings in RAST and skin tests gave a strong correlation of concordant results with the severity of the underlying disease. The highest coincidence of tests was found in patients with flour-induced asthma. The sensitivity of HR was very high when compared with RAST, skin and provocation tests. Although the assay of HR from whole blood may be a very specific indicator of cell sensitivity in the field of allergy research, the present findings indicate that the conventional methods for diagnosing flour allergy in bakers such as inhalative provocation tests cannot be replaced by this in vitro techniqu