We describe a procedure for differentiating among potential precursor responses for use in a functional analysis. Conditional probability analysis of descriptive assessment data identified three potential precursors. Results from the indirect assessment corresponded with those obtained from the descriptive assessment. The top-ranked response identified as a precursor according to the indirect assessment had the strongest relation according to the probability analysis. When contingencies were arranged for the precursor in a functional analysis, the same function was identified as for target behavior, supporting the utility of indirect and descriptive methods to identify precursor behavior empirically. (Contains 1 figure and 1 table.)