The bacteriology of the tonsillar surface and core in 30 children undergoing tonsillectomy was studied. Antibiotics taken in the six months before surgery were recorded. Haemophilus influenzae and Staphylococcus aureus were the commonest isolates; Streptococcus pyogenes was relatively rare. Eight children had received no antibiotics, the others had been prescribed 65 different courses of 13 different types. No relationship between the various antibiotic regimens prescribed and tonsillar bacteriology could be demonstrated, and it would appear that the tonsillar bacteriology at the time of tonsillectomy is not altered by antibiotics prescribed in the previous six months.