The literature dealing with monoethylhexyl phthalate (MEHP), the principal metabolite of di (2-ethylhexyl) phthalate (DEHP), a widely used plasticizer, is discussed. MEHP has been shown to be moderately toxic and, following oral administration, undergoes omega- and omega- 1 oxidation to yield the same metabolites as does DEHP. In plasma there is an equilibrium between MEHP absorbed to albumin and in free solution, whereas DEHP is bound to lipoproteins. Studies involving orally administered MEHP revealed the mild hepatic changes occurred but there was no bioaccumulation of the monoester. Studies of the rat and rabbit indicated that MEHP has no teratogenic effects.