Antipyrine disposition and metabolism in conscious, unrestrained Sprague-Dawley rats after 25% or 50% Fluosol hemodilution is reported. 25% hemodilution depressed antipyrine metabolism for 24 hours by primarily inhibiting cytochrome P-450. However, 50% hemodilution produced significant increases in the cytochrome P-450 activity after 48 hours. 25% hemodilution significantly reduced the antipyrine Vd at 0.5 and 72 hours. After 50% hemodilution, the Vd alternated between values greater and less than control throughout the 72hour study.