Experiments are described the results of which lead to the following conclusions: (1) Relatively unmusical observers can learn to increase their accuracy in assigning pitch numbers to pure tones. (2) The greatest increase in ability takes place during the first few practice sessions. (3) The limit of ability reached in this experiment was an average error of about three semi-tones. (4) The course of the learning process is irregular, and there are large individual differences. (5) Unmusical observers can learn accurately to recognize tones that are eight and one third semi-tones apart, but they fail to learn to judge the tones correctly when the interval is decreased to five and one half semi-tones or less. (6) Observers build up a subjective scale in which they can place unfamiliar tones as accurately as familiar ones. (7) Contrary to previous findings, the greatest average error in the present experiments was made in identifying tones from the middle of the scale, the size of the error gradually decreasing toward the ends. (PsycINFO Database Record (c) 2006 APA, all rights reserved)