An evaluation was conducted at the University of Iowa Health Sciences Library to determine what effect the user's presence had on MEDLINE search results. One hundred users participated over a four-month period. Three main criteria were used: search precision, search recall, and user satisfaction. Each MEDLINE search was processed twice, once prior to the user's arrival and a second time during the scheduled appointment with the user. The two searches for each user were processed by different searchers, and four searchers alternated processing the user-absent or the user-present search. Users were asked to compare the citations on the two searchers by checking each printout for relevant citations. A short questionnaire was administered to determine general information about users and satisfaction measures for each search. The extensiveness of the interview for the user-absent search was varied in order to determine if the depth of the initial interview would affect the search results. Evaluation of the findings indicated an increase in precision, recall, and user satisfaction for the user-present search. Some difficulties in designing the experiment are discussed and implications of the evaluation results are considered.