The Gene Ontology (GO) Consortium created the evidence code 'ND' to indicate 'no biological data available'. This code is used for annotations to the three 'root' terms 'molecular_function ; GO:0003674', 'biological_process ; GO:0008150' or 'cellular_component ; GO:0005575'.

In FlyBase the use of any of these three GO terms, attributed to this reference and supported by the ND evidence code, signifies that a curator has examined the available literature and sequence for this gene and that, as of the date of the annotation, there is no information supporting an annotation to any GO term in that ontology.

Previously, the 'ND' code was used with the 'unknown' GO terms 'molecular_function unknown ; GO:0005554', 'biological_process unknown ; GO:0000004' or 'cellular_component unknown ; GO:0008372' but GO merged these 'unknown' terms with the 'root' terms in October 2006.