A selective dissemination of information service based on computer scanning of Nuclear Science Abstracts tapes has operated at the Atomic Energy Research Establishment, Harwell, England since October, 1968. The performance of the mechanized SDI service has been compared with that of the pre-existing current awareness service which is based on visual scanning of journals and reports by information staff. In order to compare the effectiveness of Euratom indexing terms and words in titles for computer SDI matching, an experiment was set up in which sixty users of the mechanized service assessed NSA document notifications which were generated by matching either indexing terms and subject categories, or words in titles and subject categories, without being aware of the method of matching. The results of the comparison indicate that words in title matching can be almost as effective as matching index terms for an SDI service covering a wide range of subjects. This raises the question of whether the expense of indexing is justified. A service based on title words would have the advantage that it could be extended to make use of other data bases, or parts thereof, with little further programming or alternation of the profile formulations. (Author/SJ)