Limited information is available on the pharmacokinetics and tissue penetration of cefazolin in pediatric patients. Nine children (age 0.8-10 years) undergoing gastrointestinal operations were studied. A single dose of cefazolin, 15-26 mg/kg was given i.v. over 2-3 min at the time of induction of anaesthesia. Multiple (5-8) blood samples were collected during the operative procedure and in the recovery room. Tissue samples from the rectus abdominis muscle were obtained at the time of incision, during surgery, and at closure. The concentration of cefazolin was measured by a high performance liquid chromatographic method. Peak serum concentrations of cefazolin ranged from 85.8-269.4 mcg/ml. Serum and tissue concentrations at incision were 50.5-169.9 mcg/ml and 1.8-29.7 mcg/g; at closure the serum and tissue concentrations ranged from 17.3-60.9 mcg/ml and 1.19-29.70 mcg/g, respectively. Total clearance, apparent distribution volume, and elimination half-life of cefazolin were 1.43 +/- 0.54 ml/min/kg, 0.08 +/- 0.03 l/kg, and 1.68 +/- 0.55 h respectively. Tissue concentrations of cefazolin were maintained above its minimum inhibitory concentrations against common susceptible pathogens. Hence, the current dosing regimen of cefazolin is adequate to protect against infection in pediatric patients undergoing gastrointestinal surgery.