Grey literature is information not available through commercial publishers. It is a sizable and valuable information source for public health (PH) practice but because documents are not formally indexed the information is difficult to locate. Public Health Information Search (PHIS) was developed to address this problem. NLP techniques were used to create informative document summaries for an extensive collection of grey literature on PH topics. The system was evaluated with PH workers using the critical incident technique in a two stage field evaluation to assess effectiveness in comparison with Google. Document summaries were found to be both helpful and accurate. Increased document collection size and enhanced result rankings improved search effectiveness from 28% to 55%. PHIS would work best in conjunction with Google or another broad coverage Web search engine when searching for documents and reports as opposed to local health data and primary disease information. PHIS could enhance both the quality and quantity of PH search results.