Abstract: The method is for monitoring contamination in a stream of fiber flocks transported pneumatically in an airflow. Characteristics of entities, including contamination, in the stream of fiber flocks are detected and evaluated. Values of a first parameter and a second parameter of the entities are determined from the characteristics of the entities. An event field is provided, which contains a quadrant or a part of a quadrant of a two-dimensional Cartesian coordinate system, wherein a first axis defines the first parameter and a second axis defines the second parameter. The values of the first parameter and the second parameter determined for an entity are entered in the event field as coordinates of an event representing the entity. Thus, entities can be handled in a differentiated way.