In case you ever used the search tag [ab] ...

The [ab] search tag has been discontinued in PubMed. But don't worry! To search titles and abstracts (plus other fields), use [tw] or [textword]. To search only the Title and Abstract fields, use [tiab] or [title/abstract].

Check out the PubMed Help Search Field Descriptions and Tags for information about other ways to use 'field qualification' or 'search tags'.

For more information, see the NLM Technical Bulletin.