Studies with an emulsion formulation of ICI 35 868 (2,6-diisopropylphenol) indicate that this new formulation has anaesthetic properties in rats and mice, and haemodynamic effects in the mini-pig which are similar to those of the previously available Cremophor formulation. Administration of the emulsion formulation to dogs produced no untoward effect, whereas the Cremophor formulation produced a marked increase in plasma histamine concentration. In the mini-pig, no adverse response was produced by the repeated administration of the emulsion formulation of ICI 35 868, whereas the Cremophor formulation produced anaphylactoid responses when a second injection was given 1 week after an uneventful first exposure to this formulation. Behavioural responses in the rat suggest that the emulsion formulation may produce less discomfort on i.v. injection