Loracarbef, a member of a unique class of beta-lactam compounds (carbacephems), has excellent chemical and beta-lactamase stability, as well as documented clinical effectiveness against a broad spectrum of bacteria. Ten-day treatment regimens of loracarbef (200-mg capsule BID or 15 mg/kg/day suspension) and penicillin VK (250-mg capsule QID or 20 mg/kg/day suspension) were compared in the treatment of group A beta-hemolytic streptococcal (GABHS) pharyngitis and tonsillitis. Adults (greater than or equal to 12 years of age) were administered loracarbef (n = 58) or penicillin (n = 58) in a double-blind, randomized, parallel study of clinical and bacteriologic response to treatment. Favorable clinical responses among qualified (evaluable) patients in the loracarbef-treated group (46/47; 97.9%) were similar to those for evaluable patients in the penicillin-treated group (43/43; 100%). Forty-one of 47 (87.2%) of the evaluable loracarbef-treated patients and 100% (43/43) of the evaluable penicillin-treated patients had negative posttherapy throat cultures for GABHS. Thirty-nine evaluable patients in each treatment group were assessed 28 to 35 days after completion of therapy: 2.6% of patients in each group experienced relapse of symptoms; and 7.7% of loracarbef-treated patients had positive cultures, compared to 12.8% of penicillin-treated patients. Two (1.9%) loracarbef-treated patients with rashes and one (0.9%) penicillin-treated patient with diarrhea withdrew from the study due to these adverse events. Diarrhea, the most frequently occurring adverse event during therapy in the loracarbef group, was reported by 8.6% of the loracarbef group and by 5.2% of the penicillin group. These data support the conclusion that loracarbef is comparable in safety and efficacy to penicillin VK for the treatment of streptococcal pharyngitis and tonsillitis in adults.