Na-CPZ was administered to ten calves i.v. and i.m. at the dosages of 15 and 30 mg/Kg b.w. in order to study its pharmacokinetic parameters. Plasma protein binding was evaluated in vitro by the ultracentrifugation technique. Short half-lives were obtained after i.v. (53.61 min) and i.m. (47.71 min) administration at the dosage of 15 mg/kg b.w., similar values were obtained after i.v. (55.19 min) and i.m. (64.21 min) administration of 30 mg/kg b.w. The mean value of bioavailability (F) following the injection of both dosages was about 45%. Plasma protein binding at therapeutical concentrations was evaluated about 44%. The Authors conclude that a daily i.m. administration of 30 mg/Kg b.w. of Na-CPZ produces serum therapeutical levels for about 8 hours against the most sensitive microorganisms and 5 hours against the less sensitive ones.