This is Volume 4 of a four volume report. The project undertakes an assessment and reconciliation of attempts to value reductions in human health risks,' and it develops new methods and estimates for these values. Volume 1, is the executive summmary. Volume 2 contains a comparative assessment of work on valuing health risks. Based on the assessment, a set of interim morbidity and mortality values applicable to effects of criteria air pollutants is developed. Volume 3 reports on a study developing and applying contingent valuation techniques to the types of light symptoms often attributed to air pollution. Volume 4 reports on the design of approaches for valuing serious or life threatening illnesses.