How to retrieve homologs information in xml or json format from NCBI using gene ID?

I tried one URL:


I dont know what to add in question mark regions

  • $\begingroup$ I'm voting to close this question as off-topic because it is a pure programming question better suited for BioStars. $\endgroup$ Oct 14, 2015 at 15:59
  • $\begingroup$ I think the default format is xml. See more about EUtils here. $\endgroup$
    Oct 14, 2015 at 16:53

1 Answer 1


From Entrez Programming Utilities Help [Internet]:

Input: Any Entrez text query (&term); Entrez database (&db); &usehistory=y; Existing web environment (&WebEnv) from a prior E-utility call

To avoid the error messages, web1, and key1 can be used as terms (these are usually being used to associate with other searches), however this returns no data, probably because the ID you supplied was simply "9", and it remains unclear exactly what you're searching for in the context of other queries.

For example:


# esearch produces WebEnv value ($web1) and QueryKey value ($key1)


So whilst view-source:eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=homologene&geneid=9&WebEnv=web1&query_key=key1 is a valid query, it's not pointing to anything.


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