eSH, NLM's controlled vocabulary thesaurus, consists of sets of terms naming descriptors, arranged in a hierarchical structure that permits searching at various levels of specificity.

On the top of the MeSH hierarchy are 15 broad categories, sometimes referred to as MeSH treetops:

• Anatomy [A]
• Organisms [B]
• Diseases [C]
• Chemicals and Drugs [D]
• Analytical, Diagnostic and Therapeutic Techniques and Equipment [E]
• Psychiatry and Psychology [F]
• Biological Sciences [G]
• Physical Sciences [H]
• Anthropology, Education, Sociology and Social Phenomena [I]
• Technology and Food and Beverages [J]
• Humanities [K]
• Information Science [L]
• Persons [M]
• >Health Care [N]
• Geographic Locations [Z]

These category names may be used to search broadly in both PubMed® and the NLM Catalog. The search syntax is simple: use the category name followed by the word "category" followed by [mh]. For example:

• diseases category [mh]
• psychiatry and psychology category [mh]

The first example above retrieves all items indexed or cataloged to any of the MeSH headings listed in the 23 branches of Category C while the second example incorporates retrieval from any of the MeSH headings listed in the four branches of Category F. By definition, treetop searching yields large subsets that may be useful on their own, but are probably more effective when combined with additional search criteria.

Please note that a few of the category names are themselves MeSH headings or entry terms to MeSH headings.

In each of the following cases, the category consists of only one branch. These category names when searched will retrieve the same postings as the MeSH heading search:

• Humanities
• Information Science
• Persons
• Geographic Locations
• Physical Sciences (which is an entry term to the preferred descriptor Natural Sciences)

In other words, information science category [mh] = information science [mh].

In each of the following cases, however, the category has multiple branches. The category name is also either a MeSH heading or an entry term to a MeSH heading that is more specific. The category name search is distinctly different from the MeSH heading search for these:

• Anatomy
• Diseases (which is an entry term to the preferred descriptor Disease)
• Biological Sciences
• Health Care (which is an entry term to the preferred descriptor Delivery of Health Care)

Note the differences in the following sample PubMed and NLM Catalog searches:

Anatomy category [mh] retrieves all items indexed or cataloged with any of the MeSH headings in the 17 branches of Category A; over five million citations in PubMed and over 81,000 citations in the NLM Catalog.

Anatomy [mh] retrieves all items indexed or cataloged with any of the MeSH headings in the more specific G01.100 and H01.158.100 branches (only 13 descriptors); about 13,000 citations in PubMed and over 8,000 citations in the NLM Catalog.

By Jan Willis and Lou Wave S. Knecht
MEDLARS Management Section

Willis J and Knecht LS. Searching MeSH^® Treetops. NLM Tech Bull. 2005 Jan-Feb;(342):e8.