Histamine release from peripheral leukocytes of "Konnyaku asthmatic patients," patients with a unique occupational bronchial asthma in Japan, was measured after challenge with the antigen. There was an antigen concentration-dependent response with highly significant correlations between the maximal histamine release and the ratio of the radioallergosorbent test (RAST) of the antigen to human serum albumin. These results suggest that the histamine release test from peripheral leukocytes as well as RAST can be a useful diagnostic test in patients with bronchial asthma.