In a clinical and bacteriological study of 42 patients with acute tonsillo-pharyngitis or chronic tonsillo-pharyngitis with acute exacerbation, patients were allocated at random to receive either a 3-day course of spiramycin or a 5-day course of erythromycin, both antibiotics being given in a dosage of 500 mg 3-times daily. The median time to disappearance of patient complaints such as fever, difficulty in swallowing, sore throat, cough and mucus was 3 days in each group and there was a significant reduction from pre-treatment to normal levels in total white cell count and erythrocyte sedimentation rate after treatment. Although more patients were considered to have shown a good clinical response to spiramycin, the difference was not statistically significant. From a bacteriological point of view, however, treatment with the regimen used was considered a failure in all cases in that neither antibiotic completely eradicated the pathogens identified at the start of treatment even though, with 3 exceptions, all of the micro-organisms were shown to be sensitive to the antibiotics before and after treatment. Few side-effects were reported in either group.