After both intravenous injection and oral administration, the factor M₁ of virginiamycin was rapidly diluted or absorbed. It then disappeared from the plasma stream at a first order exponential rate with a half life of approximately 5 hours following a process of both tissue fixation and body excretion. The bile was the main route by which the antibiotic was excreted from the body. The ratio C_bM₁/C_pM₁ was nearly one, indicating that factor M₁ was not actively transported from the liver to the bile though it is extensively metabolized to large polar fragments. After oral ingestion 15-18% of the administrated factor M₁ was absorbed through the gastro-intestinal tract. Neither bile nor the lymphatic system seemed to play a role in that absorption. The experimental data emphasized the importance of the plasmatic compartment as a reservoir for the antibiotic, the rapidity of tissular fixation and the special affinity of the factor M₁ for the skin. They correlated very well with the clinical trials which revealed the efficiency of the drug in the treatment of the gram-positive bacterial infections and the rapid onset of its action.