1. demiology is needed. Criteria for validation of exposure will depend upon the pharma
2. should include low-dose sensitivity and cokinetics of the chemical and the persis
3. reproducibility of the assay as well as expo- tence of the marker in the biologic sample
4. sure specificity. Biologic markers can inte- assayed (itself a function of the turnover
5. grate exposure via multiple routes rate of the sample and repair processes).