The pronounced change in haemolytic activities observed on examining cholera isolates from different geographical areas in the Far East during 1961-64 makes it apparent that this single biochemical activity is not a reliable criterion for the separation of a biotype or subspecies of vibrio. Furthermore, the measurement of haemolytic activity is a problem of degree and may vary with different laboratories depending upon the availability or selection of media and adherence to the physical requirements of the test procedures employed. Also, it appears doubtful that any reliable epidemiological data can be derived because of the variable results obtained from serial cholera admissions occurring in the same epidemic area. The complete agreement obtained throughout the past three years with the haemagglutination and phage sensitivity tests provides two excellent methods for the rapid differentiation between the classic cholera vibrios and the vibrios isolated recently in the Far East. The rapidity and simplicity of the chicken cell agglutination test make it suitable for field work or for use by laboratories with limited facilities.