diff --git a/internal-dev/uo-ext.owl b/internal-dev/uo-ext.owl
new file mode 100644
index 00000000..1db3e0e8
--- /dev/null
+++ b/internal-dev/uo-ext.owl
@@ -0,0 +1,25 @@
+<?xml version="1.0"?>
+<rdf:RDF xmlns="http://purl.enanomapper.net/onto/internal/ext-ext.owl#"
+     xml:base="http://purl.enanomapper.net/onto/internal/ext-ext.owl"
+     xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
+     xmlns:owl="http://www.w3.org/2002/07/owl#"
+     xmlns:xml="http://www.w3.org/XML/1998/namespace"
+     xmlns:xsd="http://www.w3.org/2001/XMLSchema#"
+     xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
+     xmlns:obo="http://purl.obolibrary.org/obo/"
+     xmlns:dc="http://purl.org/dc/elements/1.1/">
+
+    <owl:Ontology rdf:about="http://enanomapper.github.io/ontologies/internal/ext-ext.owl">
+        <dc:contributor>Javier Millan Acosta</dc:contributor>
+	<dc:license>CC-BY 4.0 https://creativecommons.org/licenses/by/4.0/</dc:license>
+	<rdfs:comment>This ontology contains proposed extensions to UO, which in due course will be submitted to the ext. </rdfs:comment>
+    </owl:Ontology>
+
+    <!-- http://purl.enanomapper.net/onto/ENM_6804785 -->
+
+    <owl:Class rdf:about="http://purl.enanomapper.net/onto/ENM_6804785">
+        <rdfs:subClassOf rdf:resource="http://www.bioassayontology.org/bao#BAO_0002752"/>
+        <rdfs:label xml:lang="en">ng/μg protein</rdfs:label>
+    </owl:Class>
+
+</rdf:RDF>