End users at the Medical College of Pennsylvania enjoyed searching CD-ROM versions of MEDLINE and judged such searches "extremely useful." To assess the effectiveness of their searches, a sample of 500 search statements from Compact Cambridge (CC) MEDLINE was examined. A high proportion of search statements (224, or 45 percent) retrieved no documents. Over one-third of search statements (185, or 37 percent) contained at least one error, which usually resulted in zero retrieval for that search statement. Searchers attempting to enter Medical Subject Headings were frequently defeated by the elaborate punctuation requirement of CC MEDLINE. "Missed opportunities" were evident in over three-fourths of search statements. One-on-one instruction and library classes may increase search success, but these measures reach a limited audience. Improvement in the search software itself is needed to help searchers improve the effectiveness of their searches.