On rare occasions persons are found whose red blood cells react as D‐positive yet have anti‐D present in their serum. The usual explanation of this finding is that the red blood cells lack a portion of the D antigen mosaic and the individual has formed anti‐D directed against the missing portions of the mosaic. This paper presents details of a case that closely resembled this situation but in which it was eventually possible to prove that misleading serological results had been obtained because of the Matuhasi‐Ogata phenomenon. The specific antigen‐antibody complex responsible for the Matuhasi‐Ogata phenomenon in this case was Bgb‐anti‐Bgh. Investigation of a large number of anti‐D typing sera revealed the presence of anti‐Bg (anti‐HL‐A) antibodies in nearly 50 per cent of them. The implications of these