Abstract. Two unrelated donors possess a ‘new’ antigen of the Rh system which is associated with variant D and e genes in an Ro gene complex, and which is detected by a ‘new’ antibody, anti‐Rh 33, in serum Hawd.

Summary. Ante‐natal sera containing anti‐D and anti‐C + D antibodies were titred on an AutoAnalyzer system and the results compared with the standard manual method. A good correlation was achieved in 526 samples from 191 pregnant women. It was found that an antibody level above that of 15 International Units indicated the need for amniocentesis. One case is described where a possible bromelin inhibitor was present in the serum. The question of the method of estimating and reporting anti‐D antibody is discussed and it is concluded that until a more accurate method of measuring anti‐D in micrograms is available, International Units should be used.