A workshop to discuss progress in the standardization and control of antivenoms, organized by the Quality Assurance and Safety of Biologicals Unit of WHO, was held at the National Institute for Biological Standards and Control, Potters Bar, England, 7-9 February 2001. This was the first meeting convened by the WHO on this subject since 1979 and it brought together experts from academic institutions, antivenom manufacturers and national regulatory authorities from 21 countries. The meeting reviewed antivenom production and quality control measures and special consideration was given to the current crisis in antivenom production and supply in sub-Saharan Africa. The importance of snake bite and scorpion stings as public health issues was re-emphasised. The majority of commercial antivenoms are raised against snake or scorpion venoms.The review of antivenom production methods indicated that the vast majority of commercial antivenoms were still produced by traditional technology in horses, although some antisera were raised in sheep and rabbits. Methods used for plasma fractionation included salt and heat coagulation, caprylic acid stabilization or ion exchange chromatography, as well as immunoglobulin digestion with pepsin to produce F(ab')(2) or with papain to produce Fab fragments. The meeting agreed that there was much room for improving the production, quality control and safety profile of these products and that lessons could be learnt from the experience gained with the preparation of human immunoglobulins. Many basic assumptions, such as the need to remove Fc fragments by enzyme digestion and to freeze-dry antivenom preparations, required critical re-examination and more attention should be given to clinical trials as a means of assessing efficacy and safety and of defining the average initial dose. The Workshop also discussed concerns about the risks of transmitting infectious agents to humans via animal blood products, especially those posed by viruses or prions and it was agreed that this aspect needed attention. However, there was no documented or even suspected example of this ever having occurred in the case of antivenom treatment. Current WHO Requirements for the production and control of antivenoms and for immune sera of animal origin date from the late 1960s. The Workshop recommended that these be updated to take account of the progress that had taken place in the production and quality control of biologicals in recent years. In addition, the Workshop discussed the need for better standardization of both the venoms and antivenoms, but concluded that international standards and reference materials were not appropriate in the antivenom field due to the considerable variation in venom characteristics from the same species from region to region. Instead, it was recommended that national or regional standards be prepared and used.