Although concentration seems intuitively important for recall, it is a curious fact that the scientific study of this relation has been just about totally neglected. Reported here are four experiments designed as a beginning towards remedying this neglect. Experiment 1 showed that solving arithmetic problems intermittently during the recall interval lowered recall performance, but only to the extent that would be obtained if the time spent solving problems were simply not available for recall. The results of Experiment 2 indicated that two sets of items can be recalled only about half as efficiently as one. Experiments 3 and 4 showed that a card sorting task known to impair recall when performed during study also impairs recall when performed during recall, though not to as great an extent. In addition, Experiment 3 showed recall of words studied under two different orienting tasks to be comparably impaired by the card sorting task.