Abstract Introduction: This chapter addresses chemical aspects of occupational health and marine oil-spill response and is restricted to exposures to crude oil in its various forms. Thus in-situ burning of oil is included, but ancillary chemicals such as surfactants or bioremediation agents are not. The content of this chapter is largely based on the literature published after 1985, the date of a comprehensive review conducted by Politzer et al. [1985] for the American Petroleum Institute, and on a review carried out for the Marine Spill Response Corporation early in 1993 [Holliday and Park, 1993]. Concern about health and safety is a normal part of every oil spill. In general, safety is easier to understand and address than are concerns about exposure to crude oil and other chemicals which might be used in the response. At one level, human exposure can be addressed through the enforcement of very conservative requirements for the use of personal protective equipment (PPE). In the real world, however, conditions at a spill site make the use of such equipment inconvenient or even hazardous, and so the goal becomes to balance the risk from exposure with the appropriate level of PPE. While oil-spill cleanup is a comparatively new aspect of occupational-health practice, and dates from the formalization of response measures by companies and national and international agencies (something that occurred over the last 30 years), exposure to crude oil itself is a "mature" occupational-health matter. Workers have been exposed, both by inhalation and dermally, to the effects of crude oil for the past century. The exposure of response workers during the early phases of the oil-spill response can be likened to that experienced by oil-well-drilling crews and, to a lesser extent, by oil-well-maintenance personnel or fighters of oil-well fires. In contrast, exposures in the later stages of the cleanup are less clearly related to occupations within the oil industry. The crude oil will have been altered by weathering, and exposure to cleanup chemicals (e.g., dispersants, bioremediation agents) will become relatively more prominent. Such substances are beyond the scope of this chapter, and in any event, few data are available on the compositions or mammalian toxicity of dispersants. Although there are frequent references to toxicity in connection with dispersants, these invariably seem to refer to ecotoxicity. Human hazard does not appear to be an issue. For example, in a recently published paper entitled, "Effectiveness and safety of biosurfactants as agents of oil spill response" [Lepo et al., 1997], "safety" refers to possible toxicity to crustaceans and fish.