A new oral penem antibiotic, SY5555, was evaluated for its safety and efficacy in 35 children with various bacterial infections. SY5555 was effective in 100% of scarlet fever, pharyngotonsillitis, pneumonia, otitis media, bacterial diarrhea, urinary tract infections and skin and soft tissue infections. The etiologic bacteria were eradicated except Salmonella sp. Side effects were observed in 3.5% cases; one was diarrhea and Candida dermatitis, one was loose stool, and one was Candida dermatitis. From these data, SY5555 is thought to be a safe and effective antibiotic in the pediatric field. Regular dose of suspension preparation is 15 mg/kg/day in 3 divided dosages, and when needed the dose may be doubled.