When the cell and serum factors of a single blood stain were determined by conventional blood grouping methods it was found that each gave a different blood group reaction. An explanation is given of this apparently anomalous result, confirmed by the examination of a fluid blood sample. This case emphasises the need to check both factors in a blood stain. If serum factors alone were examined a wrong interpretation would be placed on the result. Where such a case is encountered the result is of greater evidential value, considering the relative infrequency of its occurrence.
