TO THE EDITOR: A key issue in understanding schizophrenia and in developing better drugs for the disease is whether any improvement in the negative symptoms associated with the use of neuroleptics reflects improvement not only in secondary negative symptoms but in primary negative symptoms as well. On the basis of data from a double-blind, controlled study comparing the effects of olanzapine to those of haloperidol and placebo in exacerbated schizophrenic patients (R1558281B), Tollefson and Sanger intended subsequently to determine to what extent the superior total effect on negative symptoms was direct or indirect (R1558282B). The authors defined the direct treatment effect of olanzapine as the additional improvement in negative symptoms remaining after they had corrected for changes in positive symptoms, depressive symptoms, and extrapyramidal symptoms. They found that olanzapine had a greater direct effect than placebo and haloperidol on negative symptoms, hypothesizing that this finding represented an improvement in primary negative symptoms. Some comments, however, are warranted.