This study was undertaken to determine whether the ability of group A streptococci to persist in the throat following antibiotic therapy corresponded with their capacity to adhere to and be internalised by epithelial cells. The study employed a HEp-2 cell model to examine the adherence and internalisation capacities of 42 strains (13 from asymptomatic patients with bacteriological eradication failure and 29 from patients with bacterial eradication). The adherence and internalisation efficiencies of strains from symptomless carriers were significantly higher. The average adherence efficiency of the carriers' strains was 53 (SEM 6)% versus 35 (SEM 5)% in control strains. The average internalisation efficiency of the carriers' strains was 13.4 (SEM 4)% compared with 4.4 (SE 1.6)% in the control group. The results are in agreement with the hypothesis that, in a significant number of cases, streptococcal internalisation might contribute to eradication failure and persistent throat carriage.