The pharmacokinetic data of nalidixic acid were investigated in normal and E. coli infected chickens. The highest serum concentration were reached after 2 hours with t0.5 (ab) of (1.706 +/- 0.1 min in normal and 2.030 +/- 0.11 min in diseased) and (1.72 +/- 0.11 min in normal and 1.416 +/- 0.044 in diseased chickens) following oral and intramuscular administration, respectively. The elimination half-life t0.5 (beta) were (2.514 in normal and 2.35 hr in diseased) and (2.567 hr in normal and 2.672 hr in diseased) respectively. Following intravenous injection the kinetic of nalidixic acid followed two compartments open model with t0.5 of (6.27 and 9.15 hr), Vd (0.45 and 0.79 L/kg), Cltot (8.86 and 13.32 ml/kg/min) in normal and E. coli infected chickens, respectively. Administration of nalidixic acid twice daily for 5 successive days in a dose level of 25 mg/kg b. wt. by oral and intramuscular routes showed a cumulative behaviour.