General study design and environmental considerations. Scand j work environ health 9 (1983): suppl 1, 1-7. Recent concern regarding health hazards of methylene chloride stem primarily from the discovery of its metabolism to carboxyhemoglobin. In this report, a research program is described, the purpose of which was to assess potential health effects of methylene chloride exposure in an occupational setting. Particular attention was given to evaluating possible direct and carboxyhemoglobin-mediated effects on the hematopoietic and circulatory systems. The study involved one fiber production plant which used a methylene chloride/methanol mixture and acetone as solvents and a second fiber production plant that used acetone only. The research design included a retrospective cohort mortality study and several health evaluation studies, as well as an environmental assessment of the two plants. Industrial hygiene monitoring indicated that typical methylene chloride exposures ranged from an 8-h time-weighted average of 140 ppm in areas of low methylene chloride use to a corresponding average of 475 ppm in areas of high methylene chloride use and that methanol was present in about a one to ten ratio to methylene chloride. Acetone exposures in both plants ranged from 100 to over 1,000 ppm (time-weighted average).