Reference-sample feature vectors that quantify acoustic features of different respective portions of at least one reference speech sample (44), which was produced by a subject (22) at a first time while a physiological state of the subject was known, are obtained. At least one test speech sample (56) that was produced by the subject at a second time, while the physiological state of the subject was unknown, is received. Test-sample feature vectors (60) that quantify the acoustic features of different respective portions (58) of the test speech sample are computed. The test-sample feature vectors are mapped to respective ones of the reference-sample feature vectors, under predefined constraints, such that a total distance between the test-sample feature vectors and the respective ones of the reference-sample feature vectors is minimized. In response to the mapping, an output indicating the physiological state of the subject at the second time is generated.