A total of 124 patients with lower respiratory tract (44) or urinary tract infections (80) were enrolled in an open, multicenter study to evaluate the efficacy and tolerability of sulbactam/ampicillin, administered at the dosage of 3 g/die by intramuscular route. Pretreatment pathogens from patients with lower respiratory tract infections included: Streptococcus alpha-haemolyticus in 8 cases, Streptococcus beta-haemolyticus in 2 cases, Staphylococcus albus in 7 cases, Haemophilus influenzae in 7 cases, Staphylococcus aureus in 6 cases, Klebsiella oxytoca in 5 cases, Staphylococcus epidermidis in 3 cases, Streptococcus pneumoniae in 3 cases, Escherichia coli in 2 cases; in one subject (2.75%), no microorganisms were isolated. In vitro, 36 isolates (84%) were sensitive to SA and 7 (16%) were resistant. At the end of therapy, all the causative pathogens sensitive to sulbactam/ampicillin were eliminated. In patients with urinary tract infections, pretreatment pathogens were: E. coli in 40 cases, S. albus in 16 cases, Proteus mirabilis in 8 cases, Enterobacter agglomerans in 6 cases, Proteus vulgaris in 3 cases, Streptococcus faecalis in 3 cases, Streptococcus liquefaciens in 2 cases, Pseudomonas aeruginosa in 2 cases. In vitro, 64 isolates (80%) were sensitive to sulbactam/ampicillin and 16 (20%) were resistant. At the end of therapy, 63 out of the 64 pathogens sensitive to sulbactam/ampicillin were eliminated; in one case the therapy was interrupted due to adverse effect. Clinical efficacy: in subjects with lower respiratory tract infections, sulbactam/ampicillin cured 32 patients (72.72%) and ameliorated the clinical status of 8 patients (18.18%; efficacy rate: 90.9%). As far as concerns the 80 subjects with urinary tract infections, clinical cure was achieved in 58 patients (72.5%) and improvement in 19 patients (23.7%; efficacy rate: 96.2%). Withdrawal/exclusion: 1 patient (0.8%) was withdrawn because of adverse drug effects.