AbstractThis article reports on a comparison of the postcoordinate retrieval effectiveness of two indexing languages: LCSH and PRECIS. The effect of augmenting each with title words was also studied. The database for the study was over 15,000 UK MARC records. Users returned 5326 relevance judgments for citations retrieved for 61 SDI profiles, representing a wide variety of subjects. Results are reported in terms of precision and relative recall. Pure/applied sciences data and social sciences data were analyzed separately. Cochran's significance tests for ratios were used to interpret the findings. Recall emerged as the more important measure discriminating the behavior of the two languages. Addition of title words was found to improve recall of both indexing languages significantly. A direct relationship was observed between recall and exhaustivity. For the social sciences searches, recalls from PRECIS alone and from PRECIS with title words were significantly higher than those from LCSH alone and from LCSH with title words, respectively. Corresponding comparisons for the pure/applied sciences searches revealed no significant differences.