Abstract: The antigenic fractionations and activities of Dermatophagoides farinae were determined by biochemical and immunological methods. It was found that the optical densities (OD) of the fractions had 2 peaks (Sephadex G-50) or 3 peaks (Sephadex G-200), when D. farinae extract passed through gel filtration. The immunologic activities of the fractions were measured and the results did not parallel with the quantities of proteins (values of OD). The prick test to the inhalant asthmatics showed that allergens located between the first and second peaks. Counterimmunoelectrophoresis (CIE) showed that positions of precipitating antigens were within the range of the first peak. There were more proteins but only a few antigenic fractions in the second peak. No antigenic fraction was found in the third peak.