Dr. Grandjean is an environmental epidemiologist whose research focuses on the long-term impacts of developmental exposure to environmental chemicals. In the mid-1980s, he initiated studies on marine contaminants in the Faroe Islands, where prospective birth cohort studies at first emphasized neurotoxicity, especially from methylmercury. More recent projects have examined general development and immunotoxicity in birth cohort subjects followed so far up to age 22 years. The results have had substantial public policy impact and inspired downward revisions of methylmercury exposure limits internationally. Other studies in the Faroes target age-related functional deficits and degenerative diseases, such as Parkinson's disease and cardiovascular disease, in regard to life-time exposure to methylmercury and persistent lipophilic contaminants. Research abroad also includes studies of pesticide neurotoxicity and endocrine disruption in children with prenatal exposures from their mother's work in greenhouses during pregnancy. Additional efforts relate to fluoride neurotoxicity; metal toxicology; biomarker development and validation; endocrine disruption caused by organochlorine substances; and carcinogenicity of exposure to zeolite and other mineral fibers. Occupational health studies have included research on percutaneous absorption of chemicals, carcinogenicity of fluoride exposure, and neurotoxicity of lead. Additional publications are on research ethics, genetic susceptibility, the setting of exposure limits, and the impact of the precautionary principle on prevention and research.