Normal rabbits were exposed to single, subanesthetitizing doses of chloroform vapors and a regular decrease in their total serum cholesterol was found. In rabbits with abnormally high serum cholesterol levels, however, no consistent changes were observed. In control experiments it was found that in the normal rabbit there is a diurnal variation in serum cholesterol, with lowest values around 4 p.m. No consistent changes were found in the serum cholesterol of rabbits after being submerged for brief periods in ice water.