As beta-haemolytic streptococci can be cultured in people with and in those without a sore throat, a case-control study was set up in 43 family practices in The Netherlands. The association was tested between the number of colony counts, specific T/M types and exotoxin genes and an acute sore throat. Duplicate throat swabs were taken from 663 sore-throat patients, selected by clinical criteria, and from 694 healthy controls. They were cultured for beta-haemolytic streptococci by combining several updated laboratory methods. Approximately 40% of the controls and 80% of the patients had beta-haemolytic streptococci-positive cultures. When focusing on cultures with high colony counts, not only group A (46%), but also non-group A streptococci (20%), predominated significantly in adult patients compared with controls. No T/M or exotoxin gene type was significantly more prevalent in patients than in controls. Thus, semiquantitative analysis, but not T/M and exotoxin gene typing, showed an association between beta-haemolytic streptococci and active disease. Groups A, C and G streptococci were found to be potentially pathogenic in adult sore-throat patients, and should be included in the discussion on the use of rapid antigen detection tests and penicillin treatment in primary care.