Six groups of 6 male and 6 female Sprague-Dawley rats per group were each exposed for 4 hours to atmospheres containing aerosolized THERMINOL VP-1 at ambient or heated temperatures. Exposure concentrations ranged from 1.0 to 5.3 mg of THERMINOL VP-1 vapor/aerosol per liter of air. Two additional groups of rats were exposed to house-conditioned air (either ambient or heated) and served as control groups. Exposure was followed by a 14-day observation period and subsequent necropsy. The highest mortality occurred in the 5.3 mg/1 group where 11 out of 12 animals died. No deaths occurred at 1.1 mg/1, data for calculating an LC50 for the females. During exposure observations included salivation, hypoactivity, and active animals. Immediately after exposure, notable observations included labored breathing, red encrustation about the nose and eyes, salivation, wet fur on the ventral side (due to salivation), hypoactivity, and fur coated with test material. Post-exposure observations included red encrustation about eyes and nose and opacity of eyes. By post-exposure Day 14, surviving animals appeared in good health. Decreases in mean body weights were noted in all groups except in the 1.1 mg/1 exposure concentration group and control groups. By post-exposure Day 14, all survivors had=exceeded their pre-exposure weights. Necropsy findings indicated that there were no macroscopic abnormalities which were test material-related. Based on the test results, THERMINOL VP-1 has a combined sex LC50 of 2.66 mg/1 and causes some irritation to sensory organs at concentrations of 1.0 mg/1 or greater.