The purpose of the study was to compare the efficacy of cefaclor with that of penicillin V potassium (penicillin) in patients with Group A streptococcal pharyngitis. One hundred four children with pharyngitis and serologically confirmed Group A streptococci were randomly treated with cefaclor or penicillin using a mean dosage of 20 mg/kg/day for 10 days. The difference in failure rates (14% for 51 cefaclor- and 30% for 53 penicillin V-treated patients) was statistically significant (P = 0.04). In four earlier similar studies I found that cephaloglycin, cephalexin (two studies) and cefatrizine were consistently but not significantly more effective than penicillin therapy. When the data from the five studies are combined the difference between the failure rates (11% for 263 oral cephalosporin- and 23% for 230 penicillin-treated patients) becomes highly significant (P less than 0.001). The 95% confidence interval for the odds for treatment failure are 2.4 times greater for patients receiving penicillin than for those receiving one of the oral cephalosporins. On the basis of these data I conclude that the oral cephalosporins appear to be more effective than penicillin for therapy of Group A streptococcal pharyngitis.