Because a surprisingly diverse number of potentially hazardous substances is used in conservation practice, risk assessment and its application to the control of toxic substances in the laboratory environment are topics of concern to the conservator. The processes which characterize risk are reviewed and the recommended maximum ambient concentrations for toxic substances are set (collection of epidemiological data, animal-bioassay, in vitro short term studies, development of dose-response relationships, exposure assessment in the workplace). The means by which exposure to toxic substances can be limited within a laboratory (internal monitoring of solvent concentration levels, indoor air quality, laboratory operation standards and ventilation, use of protective clothing and equipment, and personal monitoring devices) are discussed. See also AATA 21-1334 for entire proceedings.