C-reactive protein (CRP) value is usually elevated in patients with group A streptococcal (GAS) pharyngitis. The aim of this study was to describe the daily changes in CRP value after start of antibiotic treatment and to compare these changes with commonly used outcome measures in GAS pharyngitis. Eleven adult patients with sore throat and confirmed GAS infection were examined daily by specially trained medical students who registered symptoms and signs, performed a CRP test (NycoCard) and measured body temperature. At baseline, the mean CRP value was 100.3 mg/L (SD 80.9). The mean reduction after one day was 34.1% (SD 15.3), after two days 60.1% (SD 14.1) and after three days 75.3% (SD 12.5). Corresponding reductions were found for sign and symptom scores and temperature, but the standard deviations for these measures were much larger. The CRP value was significantly associated with both the symptom score and the number of days after start of treatment (p < 0.01), but not with the sign score and body temperature, as shown by multiple regression analysis for repeated measurements. The CRP test seems to be a valid test for monitoring the clinical course in GAS pharyngitis.