Recurrences are a common finding after antibiotic treatment of acute group A streptococcal tonsillitis. This has been attributed to several factors, among others a disturbed normal throat flora and especially a lack of alpha-streptococci. It thus seems logical in patients with recurrent streptococcal tonsillitis, to restore the normal alpha-streptococcal flora by reimplantation of alpha-streptococci. This was performed in a double blinded, randomized, placebo-controlled study. 36 patients with recurrent streptococcal group A tonsillitis were treated with antibiotics followed by either placebo (19 patients) or a pool of 4 selected alpha-streptococcal strains (17 patients) with good interfering activity against clinical isolates of beta-streptococci. No patient recurred during the first 2 months of follow-up in the alpha-treated group, but 7 in those treated with antibiotics and placebo. After 3 months 1 in the patient group treated with antibiotics and alpha-streptococci and 11 in the placebo-treated group recurred. These results are statistically highly significant and show that recolonisation with alpha-streptococci seems to offer a new way to lower the rate of recurrence in streptococcal throat infections.