Abstract Potentiation of haloalkane-induced hepatotoxicity by ketones and ketogenic substances is used to illustrate questions that are raised when considering biological interactions involving toxicants. The following characteristics are considered: The effect of the potentiator (ketone or ketogenic agent) on the dose-response characteristics of the haloalkane toxicant; the recovery process of the potentiated tissue injury; dose-response characteristics of the potentiators (minimally effective dosages); correlation of the potentiation with blood levels of the potentiator (threshold concentrations). The relative specificity of the haloalkanes for interaction are discussed, as well as the potentiation of various forms of hepatic injury (acute, chronic, necrogenic, and cholestatic). Enhanced bioactivation of the haloalkane toxicant is a major mechanism of action for the potentiator; other possible contributing mechanisms, however, require consideration. Mixtures of haloalkanes, leading to enhanced liver injury, can also be potentiated by ketones.