Loracarbef, a member of the carbacephem class of beta-lactam antibiotics, is a potent anti-bacterial agent. In a double-blind, randomized clinical trial to assess the efficacy and safety of loracarbef in the treatment of streptococcal pharyngitis and tonsillitis, 107 adult patients were treated with loracarbef (200 mg capsules twice a day or 15 mg/kg/day suspension) and 111 patients were treated with penicillin VK (250 mg capsules four times a day or 20 mg/kg/day suspension) for 10 days. In the loracarbef treatment group, 96.6% of the evaluable patients had a favorable clinical response 3-5 days after therapy, a result that compared favorably with the 93.9% response rate achieved in the penicillin group. The clinical failure/relapse rates were 3.4% for loracarbef-treated patients and 6.1% for patients receiving penicillin. Bacteriologic response data approximated the clinical results, with a successful response in 89.9% of the loracarbef-treated patients and 91.5% of the penicillin recipients. Two (1.9%) loracarbef-treated patients with rash and one (0.9%) penicillin-treated patient with diarrhea discontinued the study early because of these adverse events. The incidence of adverse events was comparable in the two treatment groups except for increased cough, which was reported by 3.7% of the loracarbef-treated patients and none of the penicillin recipients. These data support the conclusion that loracarbef is comparable to penicillin VK in the treatment of streptococcal pharyngitis and tonsillitis in adults.