The aim ot fhe present work was to compare the penetration in muscle tissue fluid (MTF) and muscle tissue (MT) of cephalotin administered in rabbits. Animals were distributed in Trial 1 (n = 15) and Trial 2 ( n= 6). In the Trial 1 the animals were implanted in ischiotibial muscle with non reactive material cages. Animals recibed subcutaneously (sc) cephalotin (20 mg/kg) and blood, MTF and MT samples were recollected. In the Trial 2 the animals recibed cephalotin (20 mg/kg) intravenously (iv) and blood samples were recollected. Pharmacokinetic analysis were performed using a non-compartmental model. Results: terminal disposition rate constant (λz ) (serum iv) 1.43 ± 0.54, (serum sc) 1.90, (MTF) 0.57 and (MT) 1.80 h–1 ; elimination half-life (t1/2 ) (serum iv) 0.53 ± 0.13, (serum sc) 0.36, (MTF) 1.20 and (MT) 0.38 h; the area under the curve [AUC(0-6) ] (serum iv) 60.40 ± 38.20, (serum sc) 45.90, (MTF) 21.60 and (MT) 3.00 μg.ml–1 h. and the bioavailability (F) was 76%. The penetration of cephalotin in MTF and MT were. 47.70 and 6.43%, respectively. Cephalotin administered subcutaneously in rabbit presented higher bioavailability, distribution in extracelullar fluid and low penetration in muscle tissue.