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Table of Contents: 2022 SEPTEMBER–OCTOBER No. 448

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Updated PubMed E-utilities Launching on November 15, 2022

Updated PubMed E-utilities Launching on November 15, 2022. NLM Tech Bull. 2022 Sep-Oct;(448):e4.

2022 September 14 [posted]

PubMed will be moving to an updated version of the E-utilities API on November 15, 2022. As previously announced, this updated version of E-utilities will use the same technology as the web version of PubMed released in 2020. For example, search results returned by the updated ESearch E-utility will now match those of the website.

This update only affects E-utility calls with &db=pubmed. There are no changes to the E-utilities for other databases. You can refer to our previous post or watch our recorded webinar for more details on this update.

Do I need to do anything to prepare?

  • If you manage code that creates PubMed E-utility requests, review the changes below to ensure that your code will continue to function after the update.
  • Up until launch, you can also verify your code on the public test server, available through the following URL: To use the test server, replace the standard E-Utilities URL ( in your requests with the test URL.

What will happen to the current version of the PubMed E-utilities after the release on November 15, 2022?

The current E-utility URLs for PubMed (&db=pubmed) will continue to function after the E-utilities update is released, with only a few exceptions:

  • ESearch will only be able to access the first 10,000 records retrieved by the search query (&retmax <= 10,000; &retstart + &retmax <= 10,000).
  • EPost will only be able to accept up to 10,000 PubMed IDs (PMIDs) in a single URL request.
  • EFetch will no longer support returns in ASN.1 format.

Will the output of PubMed E-utility calls be changing?

Again, in almost all cases, no. Here are the exceptions:

  • ESearch will now return exactly the same PMIDs that are currently returned by web PubMed.
  • EFetch will now return XML data by default (&retmode is not set) rather than ASN.1. In other words, the default value of &retmode will become "xml."

How can I keep in touch?

Please write to us at if you have any questions or concerns.

You can also follow the NCBI Insights Blog and subscribe to the E-Utilities Announcement Mailing List for updates. 

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