In an effort to set out the UK Patent Office's (UKPO) general practice on the patentability of inventions involving human embryonic stem cells (hES), the Office has issued a Practice Note regarding how it intends to examine such patents. Uncertainty about what can be patented in this field has arisen because the Patents Act 1977, amended to implement Biotech Directive 98/44/EC on the legal protection of biotechnological inventions, does not directly address the patentability of hES. According to the directive, human embryos for industrial or commercial purposes are not patentable. The UKPO has now drawn a distinction between pluripotent cells (those capable of giving rise to several cell types), which can be patented, and totipotent cells (those capable of giving rise to any cell type or a complete embryo), which cannot. Some view the distinction as being somewhat artificial and difficult to enforce. The UKPO says that each case will be treated on its own merits in light of all the relevant circumstances, and that the UKPO's practice is subject to any future guidance from the UK courts. UK Patent Office Practice note