Primary enduring negative symptoms (PENS) were studied in 26 patients with DSM-III-R schizophrenia and in 94 patients with unipolar major depressive episodes 5 years after the index episode. PENS were assessed with the Schedule for Deficit Syndrome (SDS). Negative symptoms were also assessed with the Scale for Assessment of Negative Symptoms (SANS) and subclassified into primary and secondary according to the SDS. The frequency of PENS did not differ significantly between schizophrenics and non-schizophrenic patients. Enduring negative symptoms (regardless of whether primary or not) were more frequently observed in schizophrenia (65% according to the SDS, and 88% according to the SANS) than in patients who had major depressive episodes (29% according to the SDS and 32% according to the SANS). By applying the SDS criteria for PENS, their frequency decreased in a manner which would probably affect the availability of patients samples for testing antinegative drugs. The results suggest that neither the negative symptomatology nor the primary enduring subtype ("deficit") is specific for schizophrenia. This finding might imply potential advantages of non-nosological, functional approaches for research into PENS.