This is a retrospective analysis of all patients with a raised titre of ANCA in a single centre over a two-year period. Sixty-five patients were identified and clinical data is presented for 58 of these-34 male and 24 female. The median age is 56 years (13-83). Fourteen patients had Wegener's granulomatosis, 14 microscopic polyarteritis nodosa and 30 had other diagnoses. The patients with unexpectedly positive results are discussed in detail. This study confirms the sensitivity of ANCA in Wegener's granulomatosis and microscopic polyarteritis nodosa but suggests that the test is not as specific as initially claimed.