Abstract This paper evaluates the retrieval effectiveness of query expansion strategies on a MEDLINE test collection using Cornell University's SMART retrieval system. Three expansion strategies are tested on their ability to identify appropriate McSH terms for user queries: expansion using an inter-field statistical thesaurus, expansion via retrieval feedback and expansion using a combined approach. These expansion strategies do not require prior relevance decisions. The study compares retrieval effectiveness using the original unexpanded and the alternative expanded user queries on a collection of 75 queries and 2334 MEDLINE citations. Retrieval effectiveness is assessed using eleven point average precision scores (11-AvgP). The combination of expansion using the thesaurus followed by retrieval feedback gives the best improvement of 17% over a baseline performance of 0.5169 11-AvgP. However this improvement is almost identical to that achieved by expansion via retrieval feedback (16.4%). Query expansion using the inter-field thesaurus gives a significant but lower performance improvement (9.9%) over the same baseline. This study recommends query expansion using retrieval feedback for adding McSH search terms to a user's initial query.