The following draft protocols were developed during a workshop funded by the European Union as a Concerted Action by DG XIV under the FAIR programme-FAIR CT 97-3760, Members of the workshop are given below and all are joint authors of the draft protocols presented here. The intention of the workshop was to bring together representatives of the major European Community laboratories (plus a limited number from outside Europe) working on aspects of the use of chemotherapeutants, particularly upon antibiotics and the problem of drug resistance in aquaculture. The primary theme of the Workshop was to enable these experts to re-examine these problems and, in particular, to discuss and gain agreement on recommendations for uniform methods for determining minimum inhibitory concentrations for the most important antimicrobials against the most important fish pathogens. The ultimate objective of this Workshop was to produce a set of recommendations on methods of determining MICs of major bacterial fish pathogens and in particular to reach agreement on the interpretation of such results in terms of resistance and sensitivity of these organisms to the major authorised aquaculture medicines.As part establishing the parameters of the workshop, some members of the workshop produced briefing reviews of the major problem areas associated with antibiotic sensitivity testing. These papers are presented here, following the draft methods developed in the workshop.Aquaculture is subject to a range of widespread bacterial diseases, which reduce its efficiency. Some of these diseases can be controlled by effective vaccines, but under the multiple stresses of intensive aquaculture, this protection can break down. Under these circumstances and for many of those pathogens for which vaccines are not yet available, chemotherapy remains an essential aid to reduce losses and improve animal welfare.Within the Community (and indeed outside it) the range of authorised antimicrobials which are available for aquaculture use is very limited, and with tightening of the controls on the use of veterinary medicines and on the presence of residues in fish tissues, this range is unlikely to increase significantly. This means that we need to ensure that what is available is used most efficiently to reduce the selection pressure for drug resistance. Published by Elsevier Science B.V.