Pharmacokinetics, in vitro, and in vivo effect of aztreonam (SQ 26,776, AZT), a newly synthesized monobactam antibiotic, were investigated in pediatric patients. The pharmacokinetics were studied in 12 children without renal or hepatic impairment, each of whom received single 10, 20 and 40 mg/kg intravenous doses of drug. Serial samples of serum and urine were assayed for AZT. Serum pharmacokinetics of AZT were described by an open, linear, two-compartment kinetic model. After intravenous administration, AZT was eliminated primarily by urinary excretion of unchanged drug (60.4%). The average biological half-lives of AZT in serum were 1.33 (10 mg/kg, n = 1), 1.69 +/- 0.40 (20 mg/kg, n = 8), and 1.51 +/- 0.61 (40 mg/kg, n = 3) hours. The antibacterial activity of AZT against E. coli and P. aeruginosa was equal or slightly stronger than that of CPZ, LMOX, and CTX. It had no antimicrobial activity against Gram-positive cocci. In vivo effect of AZT was evaluated in 13 children with various infections. The result was excellent in 7 cases, good in 1 case, fair in 3 cases and poor in 1 case, with effective ratio of 66.7%. Exanthema or elevation of GOT and GPT were noticed in 3 patients.