Phee calls were recorded from five captive common marmosets on three occasions. An initial recording session was followed by further sessions 1–12 days later, and finally, 12 months after the initial sample. Sonograms from the first recordings were measured using one duration and five frequency parameters, and significant differences between individuals were found for all six parameters. Discriminant function analysis was then applied to classify each call to a particular individual, witn a resulting classification accuracy of 97.27%. Analysis of the second and third recordings demonstrated accurate classification to the same caller using the measurements obtained from the initial sample. The accuracy remained high despite intra-individual differences in acoustic structure among the three recording periods. Such differences may well reflect proximate changes in the underlying arousal state of the caller. Stability over time in the vocal signature of the phee call supports the view that this vocalization may be important in signalling individual identity over long distances, in a habitat where visual contact is limited. © 1993 Wiley-Liss, Inc.