6 experiments varied intertrial interval and interitem similarity in free learning or in paired-associate learning. Facilitation by DP distributed practice was found only as an interlist effect, but this effect occurred only under certain situtations. It occurred when paired-associate learning followed free learning of trigrams with low intralist similarity but not when the intralist similarity was high. In another situation it occurred when Ss were not naive, but did not occur when they were. No facilitation was found for DP in free learning. The particular locus (response-learning phase or associative phase) of the DP effect in paired-associate learning could not be identified. Other findings included: poorer performance in free learning for high-similarity units than for low, for both paced and unpaced recall; no effect of DP on 24-hr. retention; no difference in recall of paired-associate lists when the response terms were or were not shown on the recall trial.