This document describes the general requirements to be taken into account in planning and implementing plant-related plume measurements of microbial air pollutants. A basic principle of this method is to compare the concentrations in air unaffected by the activities of the plant (i.e. background air sampled upwind of the plant) with the concentration of bioaerosols in air downwind of the plant. It is this comparison that allows an assessment of the plant-related contribution and the mean spatial impact range to be made. As it has so far not been possible to set limit values based on dose-response relationships, the mean impact range is to be used as a first criterion for assessing the environmental impact of a plant. The scale of work for the plume measurements described is necessary to obtain statistically representative data about the impact range of the plant and/or source, taking into account the great variety of influencing factors. Plant-related measurements of bioaerosol concentrations in ambient air may be required in a number of regulatory situations. Examples of typical measurement objectives and indicative application scenarios are presented in the document. This method specifies the simultaneous measurement of background and downwind air quality to reduce the risk of invalid comparisons resulting from changing background air concentrations. Another important principle of this method is the requirement for repeated measures to take into account day to day and seasonal variations in the processes governing bioaerosol emissions and dispersion. The objective is to analyse a given measurement problem and derive the associated requirements for organization, the measurement method, the sampling strategy, the evaluation of the measured data, quality assurance and reporting.