An exposure standard is proposed for the vinyl halides and evidence gathered to support the standard is reviewed. It is proposed that employee exposure to vinyl halides in the workplace be controlled by adherence to the provisions for vinyl-chloride (75014), which are appended. The recommended standard applies to workplace exposure to the monomers vinyl-chloride, vinylidene-chloride (75354), vinyl- bromide (593602), vinyl-fluoride (75025), and vinylidene-fluoride (75387), including any unreacted monomer that may remain in polymers of these halides. The biologic effects of exposure to humans, including epidemiologic studies and historical reports of exposure are reviewed. Studies of animal toxicity and metabolism of these compounds, structure activity considerations, and correlation of exposure and effect are examined. Studies of carcinogenicity, mutagenicity, teratogenicity, and reproductive effects are described. Results show the biologic effects of vinyl halide exposure to include changes in behavior, cardiovascular abnormalities, degenerative changes in the liver and bones, and the induction of malignant neoplasms, especially angiosarcomas of the liver. Sampling and analytical procedures for airborne vinyls in occupational environments are described. Results of vinyl-chloride production workplace hygiene studies are reported. Engineering controls to eliminate the potential for exposure to vinyl halides are discussed. Closed system operations are recommended as providing the best means of elimination of employee exposure, but ventilation systems are also examined. Safe work practices and personal protection are discussed. The basis for previous vinyl halide standards and the recommended standard are examined. It is noted that only vinyl-chloride is a known human carcinogen at this time, but animal studies suggest the possible efficacy of the other vinyl halides in this regard. Research needs on biological effects of exposure to vinyl halides include epidemiological studies, examination of human toxic effects, and development of sampling and analysis practices, particularly for vinyl halides other than vinyl- chloride. A substantial bibliography is appended.