The pharmacokinetics of cephalexin was investigated in male calves following a single intravenous (i.v.) and subcutaneous (s.c.) administration (10 mg/kg). The distribution rate constant and distribution half-life were 3.34 +/- 1.22 h-1 and 0.32 +/- 0.08 h, respectively. The values of elimination half-lives following i.v. and s.c. administration were 3.17 +/- 1.30 and 2.56 +/- 0.24 h, respectively. The absorption half-life following s.c. administration was 0.09 +/- 0.01 h. The apparent volume of distribution was 0.65 +/- 0.16 and 0.46 +/- 0.07 L/kg and total body clearance was 2.96 +/- 0.46 and 1.66 +/- 0.31 ml/kg/min, respectively, following i.v. and s.c. administration. Systemic availability following subcutaneous administration was found to be almost complete (103.08%). The satisfactory intravenous dosage regimen of cephalexin for calves would be 11.3 mg/kg as the priming dose followed by 10.0 mg/kg as the maintenance dose to be repeated at 6-h intervals. However, the subcutaneous dosage regimen of cephalexin in calves would be 8.0 mg/kg followed by 7.05 mg/kg at 8-h intervals.