In order to evaluate efficacy and safety of L-Keflex (granule form of sustained release cephalexin), a double blind study comparing it with Keflex (capsule of regular cephalexin) was conducted in dental infections. Evaluable cases in adults for efficacy of the drugs were 196 consisting of 97 for L-Keflex and 99 for Keflex. Those in children were 19 (8 for L-Keflex and 11 for Keflex). There were no significant differences in background of the patients and severity of the diseases between both groups (L-Keflex and Keflex groups). The daily doses used in both groups were 1,000 mg in adults and 500 mg in children, respectively. The dose was given in two divided doses for L-Keflex group and in four divided doses for Keflex group. Following are evaluation by the committee members for the study: Adults 1. Clinical response rate at final therapy day was 93.8% in L-Keflex group and 92.9% in Keflex group, showing no significant difference between both groups. 2. No significant difference in severity of subjective and objective symptoms between both groups was observed at each therapy day. 3. Side effects were found in 6.7% of 105 patients receiving L-Keflex and in 5.6% of 107 patients with Keflex, and there was no significant difference between both groups. As the side effects, gastrointestinal symptoms, rash and itching were observed, but no any other side effects were found in both groups. Children 1. As shown in the above, number of the cases enough to evaluate statistically was not obtained, but all of both groups clinically responded to the drugs. 2. As for side effects diarrhea was observed in only one patient of Keflex group consisting of 12 patients. In the patient, however, discontinuation of the drug was not required and the side effect disappeared during the therapy. From the above results, L-Keflex (granule) is judged to have more convenience than Keflex (capsule) in that (1) it can be administered with b.i.d. regimen and (2) it can be easily taken in dental patients such as patients having difficulty in opening mouth of swallowing pain.