Antiperinuclear factors (APF) are directed to epithelial cell "kerato-hyaline granules". Standardization of the APF test has been achieved, but the way to express the results is still debatable. APF were found to be present in 76% of rheumatoid arthritis (RA) patients: thus the sensitivity and the specificity for RA were 76 and 97%, respectively. No clinical or serological associations were substantiated in RA. The antigens targetted by these auto-antibodies are extremely variable from one to another donor.