AbstractAfter one year's operation of a Selective Dissemination of Information (SDI) program for personnel of the Air Force Materials Laboratory, the program was evaluated by personal interview. Although most people were receiving pertinent abstracts, they were also receiving many nonpertinent abstracts. The exposure to periodic distributions of abstracts permitted the recipients to identify factors causing nonpertinent retrievals. In an experiment, the profiles were modified by applying Boolean NOT logic to terms identified as causing non‐pertinent retrievals. The uniqueness of the approach is the systematic application of the Boolean NOT to profilesafterthe SDI users had examined all abstracts from the original profiles and rejected nonpertinent returns. Retrieval results obtained by both the original and modified profile strategies for the same document base were compared. The SDI users assessed the relevance of the documents retrieved under both conditions. Precision was markedly improved by the modified strategies, although some loss of relevant documents also occurred. A follow‐up study indicated greater user satisfaction with modified profiles; fewer nonpertinent abstracts were being received, yet the number of pertinent retrievals did not appear to be diminished. The careful use of the Boolean NOT technique applied to SDI profiles to improve precision was thus substantia