This article provides a brief history of the development of the field of immunotoxicology from one individual perspective and separates the discussion into five phases: the methods development and validation phase; the compound testing phase; the many meetings and organization of the specialty section phase; the mechanistic studies phase; and the guidelines phase. During the discussion of each phase, major highlights, accomplishments, contributors and key references are provided. The immunotoxicology guidelines for the testing of pharmaceutical chemical entities across the three major geographic axes are also presented and compared, along with some of the concerns raised by industry with these guidelines. The mandatory requirement of functional tests represents the major concern and difference between the Committee of Proprietary Medicinal Products (CPMP) and the new Food and Drug Administration (FDA) guidance. The scientific basis for the recommendation of the functional tests proposed in the guidance documents based on National Institute of Environmental Health and Safety/National Toxicology Program (NIEHS/NTP)-sponsored studies is described. Experience at Sanofi-Synthelabo, with the testing of 29 new chemical drug entities developed across a broad range of therapeutic classes using this testing paradigm and functional tests to define their immunotoxic potential, yielded a low number of compounds (6.8%) that produced any abnormal reaction. The two positive compounds might have been anticipated based on their pharmacology.