The NIH has revised their policy for submissions to require the PubMed Central reference number be included in documents submitted to the NIH.
To facilitate downloading of reference information to PMC, EndNote filters, files, and an NIH output style have been revised to place the PMC number in the Custom 2 field for the Journal Articles. Instructions and downloads are available here.
NLM has created a converter to help locate the PMC ID from the PMID and vice versa.
, November 12, 2008