The pharmacokinetics of ceftazidime (CAZ) were studied in lactating (LTG) and non-lactating (NLTG) cows. Two groups (LTG and NLTG) of 5 healthy dairy cows were given ceftazidime (10 rag/ kg body weight) intravenously (i.e.) and intrammeularly (i.m.). Serum and milk (LTG) and serum samples (NLTG) were collected over a 24-h period post-administration. CAZ concentrations in serum and milk were determined by high-performance liquid chromatography, and an interactive and weighted-non-linear feast-squares regression analysis was used to perform the pharmacokinetic analysis. The pharmacokinetie profiles in LTG and NLTG cows which had received CAZ i.e. fitted a three-compartment model and a two-compartment model, respectively. The CAZ concentration-time curves in serum and the area under the curve were greater and more sustained 07<0.05) in the LTG cows by both routes, while the serum clearance (CI, = 72.5 + 18.1 ml/h per kg) was lower 07 < 0.05) than that in the NLTG cows (CI, = 185.9-1-44.2 ml/h per kg). CAZ given i.e. exhibited a relatively long halflife of elimination (t~ I~ (LTG)= 1.1+0.2 h; t~ ~ (NLTG)= 1.4-1-0.3 h). Compared with other cephalosporms, CAZ 'had good penetration rote the mammary gland (47.7__.38.2% for CAZ t.v.; 51.14-39.0% for CAZ i.m.). Finally, the bioavailability of CAZ (F(LTG)=98.9+36.8%; FfNLTG) = 77.1 4-25.3%) was suitable for its use by the i.m. route in lactating and non-lactating cows.