Anti-R23.1 and anti-R24.1 MAbs recognise a 21 kDa plasma membrane and cytoplasmic protein expressed by HL and aggressive NHL that is identical to CYB5B, a protein that has been putatively named as an outer membrane mitochondrial protein based on partial similarities to CYB5A, an endoplasmic reticulum tail-anchored protein and high sequence identity with rat outer membrane mitochondrial protein rOM b5. This evidence concerns the gene CYB5B and Hodgkins lymphoma.