| OAINN | Ohio Aerospace Institute Neural Networks | - | Medical |
| OBER | Office Of Biological And Environmental Research | - | Medical |
| OHER | Office Of Health And Environmental Research | - | Medical |
| OMIM | Online Mendelian Inheritance In Man | - | Medical |
| OPRR | Office Of Protection From Res. Risks | - | Medical |
| ORAU | Oak Ridge Associated Universities | - | Medical |
| ORDA | NIH Office Of Recombinant DNA Activities | - | Medical |
| ORF | Open Reading Frame | - | Medical |
| ORISE | Oak Ridge Inst. For Science And Education | - | Medical |
| ORNL | Oak Ridge National Laboratory | - | Medical |
| OSU | Oregon State University | - | Medical |
| OTA | Office Of Technology Assessment | - | Medical |
