2-Ethyl-1,3-hexanediol (EHD), an insect repellant, was found to have acute peroral LD50 values in the rat of 9.85 ml/kg (males) and 4.92 ml/kg (females). Acute percutaneous LD50 values in the rabbit were 10.8 ml/kg (males) and 9.51 ml/kg (females). There were neither deaths nor signs of toxicity during or following a 6 hr exposure to a statically or dynamically generated substantially saturated vapor atmosphere. A 4 hr exposure to a high concentration (3.8 mg/liter) of a respirable aerosol of EHD (mass median aerodynamic diameter of 2.0 um) produced only minor signs of irritation during exposure, but no signs of toxicity. Occluded dermal contact with EHD on rabbits (4 and 24 hr) produced mild local erythema and, in several animals, edema. Contamination of the eye with EHD (0.005 to 0.1 ml) produced marked to severe conjunctivitis, with moderate iritis and diffuse corneal injury; healing occurred in most animals within 3 to 7 days. The major acute hazards with EHD are by swallowing and, to a greater extent, by contamination of the eye.