The plastic impression method to assess the number of active palmar sweat glands (PSI) was used to study changes of sweat gland activity during several phases of dental treatment. Subjects were 64 female and 38 male patients at a dental surgery. At the beginning they scaled five typical dental situations in terms of perceived threat: waiting-room before treatment: sitting down in the dental chair; dentist enters and starts treatment; after treatment in the dental chair; and back in waiting-room after treatment. Four prints were taken in the waiting-room before treatment and one in each other situation described above. The average of prints 3 and 4 was used for phase comparisons. Palmar sweat index values were generally in accordance with the threat of the situations. In particular there was a rise from waiting-room to sitting down in the dental chair and a further increase at the dentist's entry, whereafter values dropped considerably. A significant decrease from the first two waiting-room values to the following two suggests that the PSI reacts sensitively to the novelty of the assessment procedure itself and that the very first recordings should hence not be taken into evaluation.