The efficacy and safety of ertapenem, 1 g once a day, for the treatment of community-acquired pneumonia (CAP) requiring parenteral therapy were compared with those of ceftriaxone, 1 g once a day, in 866 hospitalized adults randomized in two prospective, double-blind, multicentre studies. Patients were stratified according to Pneumonia Severity Index (< or = 3 or >3) or age (< or = 65 or >65 years). After > or = 3 days of parenteral antimicrobial therapy, patients who had clinically improved could be switched to oral co-amoxiclav. The median durations of parenteral, oral and total therapy in the 658 clinically evaluable patients, of whom 88% were switched to oral therapy, were 4, 7 and 12 days, respectively, in both treatment groups. The most common pathogen was Streptococcus pneumoniae, of which 79% (143/181) were penicillin susceptible and 3.3% (6/181; three in each treatment group) were penicillin resistant. Cure rates for the two treatments were equivalent: 91.9% for ertapenem and 92.0% for ceftriaxone (95% confidence interval for the difference, adjusted for strata: -4.5 to 4.4). Cure rates in the different severity and age strata and bacterial eradication rates for both treatment groups were also similar. The most common drug-related adverse events in both treatment groups were diarrhoea and mild-to-moderate elevations in aminotransferase levels. The results of these studies demonstrate that ertapenem, 1 g once a day, was highly effective therapy for CAP in hospitalized adults with moderate-to-severe disease.