C-reactive protein (CRP) and full blood counts were performed on 60 consecutive patients admitted with right iliac fossa pain. Of these, 31 patients had appendicitis and six had a negative appendicectomy. The CRP was raised in 29 (94%) patients with appendicitis and was not raised in five (83%) patients who underwent a negative appendicectomy. In the cases of appendicitis the CRP was significantly raised more often than the white blood cell count (WBC) (P less than 0.05, chi 2 = 3.98). In 30 (97%) patients who had appendicitis the CRP or white blood cell count was elevated. CRP is of value in indicating acute pathology and its routine performance may decrease the negative appendicectomy rate.