The International Conference on Harmonisation (ICH) process considers ways in which the technical requirements for assuring the quality, safety and efficacy of medicines can be made more compatible. At present, divergencies can make it necessary for companies to repeat tests or present the data in different formats to satisfy the requirements of different health authorities. In this context, I report that agreement on Step 2 of an ICH guideline on stability testing of biotechnological/biological products has been reached. This guideline will be of significant benefit in reducing the need to repeat costly and lengthy storage trials for biologicals to meet differing requirements. This guideline will be an annex to the ICH Harmonized Tripartite Guideline on Stability Testing of New Drug Substances and Products published in 1993. According to its present scope it covers vaccines consisting of well-characterized proteins and polypeptides and conventional vaccines after consultation with the appropriate regulatory authorities. The purpose of stability studies is to establish how the quality of a drug substance (bulk material) and a drug product (final container product) varies with time under the influence of a variety of environmental factors such as temperature, humidity and light, and enables recommended storage conditions, re-test periods and shelf lives to be established. The guideline contains specific advice for the selection of batches, the stability-indicating profile, storage conditions, testing frequency, test procedures and test criteria, specifications, long term-, stress- and accelerated testing, labelling, etc. and a glossary which defines certain of the traditional terms used in the biologics field. Therefore, it will help in informing the industry and the regulatory authorities of the important factors in stability testing of biological/biotechnological products.