Journal articles often indicate support of the reported research by a funding agency. When the funding support is from the Public Health Service (PHS) agencies of the United States Federal Government, the National Library of Medicine (NLM) has routinely included the grant or contract number(s), as published in the journal article, in the MEDLINE/PubMed citation since 1981.
The National Institutes of Health (NIH) is part of the PHS; PHS also includes the Centers for Disease Prevention and Control (CDC) and the Food and Drug Administration (FDA) among other agencies.
PHS grant/contract numbers in PubMed consist of three components:
- the grant/contract number,
- a 2-letter code for the funding agency, and
- the abbreviation for the funding agency.
The PubMed Citation and MEDLINE displays show these numbers. Here's an example:
Authors and publishers present the grant numbers in a variety of formats. NLM does not attempt to standardize the format of the published grant numbers. The data are only as accurate as the original source. [Editor's Note: In July 2006, NLM edited the prefix of NIH grants numbers in citation data to change the letter 'O' to the number '0' (zero) because the number is the correct format, e.g.: RO1 was changed to R01. At the same time, NLM instituted data entry validations to enforce the number in newly created citations. This means that the grant number data in the online citations may no longer match what is in the published article, which was generally published incorrectly.] However, additional search access points are generated to facilitate searching in PubMed.
nhlbi [gr] retrieves over 187,000 citations
All citations from the former search are part of the latter search. The latter search also retrieves citations indicating NHLBI support using one of its other codes (e.g., HV, HB). The list of 2-letter grant codes is found through the Appendices of the PubMed Help or at this URL: 
The NIH Public Access plan enables NLM to associate NIH grant numbers with author manuscripts submitted to PubMed Central®. The grant numbers derived from this process are also included in PubMed citations to the final, published article. NLM began to add these grant numbers on March 24, 2006. This may result in multiple versions of the same intellectual number on one citation (some from the published article and some from the NIH Public Access submission). For example, the spacing, punctuation, or ending numbers that indicate the funding year may vary.
It's important to note that indexers add MeSH headings based on the information found in the published article. For this reason, the corresponding Research Support, N.I.H., Extramural or Research Support, N.I.H., Intramural headings (or Research Support, U.S. Gov't, P.H.S. heading prior to June 2005 data entry) will not be added to the citations if the grant number is derived only from the NIH Public Access submission process. NLM also does not routinely add a heading before its introduction date. A comprehensive search for NIH-supported research must, therefore, include the 2-letter codes and agency abbreviations as well as the MeSH headings.