An experiment was conducted to identify some of the important parameters affecting search time, a critical cost factor in retrieval systems. Using actual computer searches of Chemical Abstracts Condensate, a comparison was made between the effectiveness of linear and inverted filing systems. Since the results indicated that it was the type and number of questions which determined which filing system was most practical, it was hypothesized that the optimal retrieval system would incorporate both linear and inverted files and would include a program to determine which filing system would facilitate the fastest search. Contained in the text are reviews of relevant literature, a detailed description of the experiment, and tabular data to support the analysis. (EMH)