| Omics | http://edamontology.org/topic_3391 | Omics | |
| Oncology | http://edamontology.org/topic_2640 | Oncology | |
| One channel microarray | http://edamontology.org/topic_3518 | Microarray experiment | |
| Ontologies | http://edamontology.org/topic_0089 | Ontology and terminology | |
| Ontologies, nomenclature and classification | http://edamontology.org/topic_2829 | Ontologies, nomenclature and classification | |
| Ontology | http://edamontology.org/topic_0089 | Ontology and terminology | |
| Ontology and terminology | http://edamontology.org/topic_0089 | Ontology and terminology | |
| Operon | http://edamontology.org/topic_1311 | Operon | |
| Opthalmology | http://edamontology.org/topic_3417 | Opthalmology | |
| Optometry | http://edamontology.org/topic_3417 | Opthalmology | |
| Organelle genes and proteins | http://edamontology.org/topic_0616 | Organelles | |
| Organelles | http://edamontology.org/topic_0616 | Organelles | |
| Organic chemistry | http://edamontology.org/topic_3314 | Chemistry | |
| Organisms | http://edamontology.org/topic_0621 | Model organisms | |
| Orthopaedics | http://edamontology.org/topic_3416 | Musculoskeletal medicine | |
| Otolaryngology | http://edamontology.org/topic_3406 | Ear, nose and throat medicine | |
| Otorhinolaryngology | http://edamontology.org/topic_3406 | Ear, nose and throat medicine | |
| Paediatrics | http://edamontology.org/topic_3418 | Paediatrics | |
| Pain medicine | http://edamontology.org/topic_3401 | Pain medicine | |
| Parasitology | http://edamontology.org/topic_3302 | Parasitology | |
| Pathogens | http://edamontology.org/topic_0783 | Pathogens | |
| Pathology | http://edamontology.org/topic_0634 | Pathology | |
| Pathways | http://edamontology.org/topic_0602 | Molecular interactions, pathways and networks | |
| PCR | http://edamontology.org/topic_0195 | Virtual PCR | |
| PCR experiment | http://edamontology.org/topic_3519 | PCR experiment | |
| Peptide identification | http://edamontology.org/topic_0121 | Proteomics | |
| Peptides | http://edamontology.org/topic_0154 | Small molecules | |
| Peptides and amino acids | http://edamontology.org/topic_0154 | Small molecules | |
| Peptides and amino acids | http://edamontology.org/topic_0613 | Peptides and amino acids | |
| Personal genomics | http://edamontology.org/topic_0622 | Genomics | |