Two experiments were performed to investigate one facet of the question of discriminability of melodic sequences in just intonation and equal temperament. First an ABX test was given to 20 listeners, in which prerecorded ascending diatonic scales of each type were used. Two widely different timbres were used, one flutelike and the other spectrally complex. Only three subjects gave results significantly different from chance. A second experiment employed scales deviating from equal temperament in a manner similar to the just scale, but varying in amount from −6 to −30 cents on the third, sixth, and seventh steps (mi, la, andli). These were compared to equally tempered scales by both ABX and AX procedures. Results showed that the maximum difference between the just and equally tempered scales (16 cents) lies just below the “ABX threshold,” but above the “AX threshold.” It is significant that music students used here (admittedly well conditioned to equal temperament) said that when they. were certain of a discrimination, it was because one of the scales contained tones which were “too flat.”