Discrimination of two types of simulated single-second-formant frequency transitions was studied, transitions where members of a stimulus set shared the same onset frequency and transitions where stimuli of a set ahared the same offset frequency. Experiment 1 employed an adaptive procedure to measure just-noticeable differences for transitions that increased in frequency. Experiment 2 obtained complete psychometrie functions, based on a three-interval, forced-choice procedure, for transitions that either increased or decreased in frequency. In both experiments, better discrimination occurred for longer stimuli, measured in hertz/millisecond, and for transitions that shared the same onset frequency. There were no differences, in Experiment 2, between discrimination of rising and falling transitions, Results are considered from several theoretical perspectives.