A double-blind study of 134 pediatric outpatients with acute streptococcal pharyngitis demonstrated that cyclacillin, administered three times a day for ten days, is as effective as a similar regimen of amoxicillin. Clinical success was achieved in 95% of the children treated with either drug. A bacteriological cure was seen in 82% of the children evaluated in the cyclacillin group and 90% of those evaluated in the amoxicillin group. The mean time required for remission of signs and symptoms in the respective treatment groups was 3.1 and 3.0 days. Only two patients (3%) in each treatment group experienced an adverse effect of the prescribed drug.