An open, non-comparative multicentre study was conducted at 36 sites in six countries to test the efficacy and safety of piperacillin/tazobactam in the therapy of lower respiratory tract infections. Piperacillin 4 g and tazobactam 500 mg were administered intravenously every 8 h for a minimum of five days. Two hundred and thirty patients were enrolled: 133 were evaluable for clinical efficacy and 106 for bacteriological efficacy. The clinical response was favourable in 96% of evaluable patients and the bacterial eradication rate was 93%. Nine patients (4%) had severe adverse events related to piperacillin/tazobactam and requiring discontinuation of therapy. In this study piperacillin/tazobactam was an effective and safe drug in the treatment of hospitalized patients with lower respiratory tract infection caused by sensitive organisms.