We have investigated plasma kallikrein amidolytic activity in the following groups of patients: 1. Normal control group of blood donors. 2. Extrinsic pollen-activated bronchial asthma patients, during periods of symptomatology and at a later time after the spring. 3. Subjects with atopic bronchial asthma in acute phase when admitted to our hospital's emergency room and later when clinically recovered. 4. Subjects with extrinsic bronchial asthma, sensitive to Dermatophagoides pteronyssinus and Dermatophagoides farinae with FEV1 < 80%. 5. Subjects with extrinsic bronchial asthma, sensitive to Dermatophagoides pteronissinus and Dermatophagoides farinae in a state of clinical rest. After 9 minutes of activation, the following results were found, with a significance of p < 0.01: There are significant differences between the normal group and those that we consider the active groups, asthma FEV1 < 80%, pollen-sensitive asthma in springtime and acute asthma. No significant differences exist between the normal group and inactive groups, inactive asthma, pollen-sensitive asthma out of springtime and acute asthma inactive. Significant differences exist in active groups (acute asthma and pollen-sensitive asthma in springtime) when they become inactive (acute asthma inactive and pollen-sensitive asthma out of springtime). The active groups have a higher plasma kallikrein amidolytic activity than both the inactive and control groups.