The main objective of this work is to review methods for the assessment of bioaerosols and consider some of the problems which arise. This paper investigates the main techniques currently available for sampling and detecting airborne microorganisms, examines a number of factors which can affect their survival, and discusses problems associated with the production of test bioaerosols. Ultimately it is hoped that a better understanding of these will provide a basis for the development of standard assessment protocols for bioaerosols and also help in the establishment of bioaerosol standards. The need for aerobiological monitoring in occupational hygiene, containment of bioprocessing equipment, deliberate release of microorganisms, contamination of food and pharmaceutical products and general scientific research, has been identified. Despite the fact that aerobiological monitoring has wide application and may be carried out to comply with guidelines or regulations there are, at present, no standard protocols for sampling airborne microorganisms. Six criteria, which need to be considered when carrying out any aerobiological monitoring, have been identified and defined. Samplers used to collect bioaerosols are described and areas of their application highlighted. Few have been fully characterised in terms of their inlet or bioefficiencies. Samplers not currently used but which have potential use in bioaerosol monitoring have also been identified and described. A series of microbial assay methods are described in terms of their sensitivity, speed, and their relationship with the choice of sampler. The interdependence of sampling and assay methods is discussed. Methods for the production of bioaerosols, from both liquid suspension and dry powder, are described. Techniques for the controlled production of poly and monodisperse aerosols are discussed. The survival characteristics of microorganisms are considered because they can greatly influence the effectiveness of sampling and assay methods. A number of recommendations and a programme of research work are outlined in order to further the understanding of the characteristics, behaviour, and assessment of bioaerosols prior to consideration of the possible establishment of bioaerosol standards for test purposes.