AbstractWe have utilized [3H]diacetyl-didemnin B([3H]DB) in a series of in vitro experiments to determine the time course of equilibration of[3H]DB between plasma and blood cells, the distribution of [3pH]DB among blood cells, and the distribution of [3H]DB in plasma. Within 45-60 min at 37d`C, approximately 55% of[3H]DB added to whole blood remained in the plasma. Of the drug associated with blood cells, 77% was found with the red blood cells, 18% with the lymphocytes, and 5% with the granulocytes. However, on the basis of amount of drug uptake per cell, lymphocytes incorporated nearly 400 times more and granulocytes nearly 30 times more [3H]DB than red blood cells. No specific association of [3pH]DB with a particular lymphocyte subset was detected. Additionally, it appears that [3H]DB in plasma was associated to a large extent with albumin.