Animal studies have shown that SQ 26,776 (SQ), a novel monocyclic β -lactam, is metabolically stable, exhibits good pharmacokinetic properties and is highly efficacious in experimental infections. When administered to mice and rats (50 mg/kg, sc), peak serum levels are in excess of 100 mg/l. In squirrel monkeys given 10 mg/kg im, a peak serum level of 34 mg/l is achieved. Urinary excretion in the 3 species approaches 50% in the first 6 h. In rodents 13% is recovered in the bile. The compound is well distributed in tissues with high levels being detected in liver, kidney and genital tract. Protein binding in human serum is 27%. In systemic murine infections involving Pseudomonas aeruginosa SQ demonstrated superior efficacy to cefotaxime and piperacillin. With infections caused by members of the Enterobacteriaceae , SQ was equivalent or superior to cefotaxime. Against Haemophilus influenzae meningitis in neonatal rats SQ showed equivalent efficacy to cefotaxime but was superior in mouse wound infections involving β -lactamase producing Proteus rettgeri and Serralia marcescens .