The study described in the letter by Volavka et al retrospectively examined pHVA concentrations in 28 schizophrenic subjects. This sample was "selected" from a larger sample of 176 schizophrenic patients who were assigned to three plasma levels of haloperidol for 6 weeks. The authors used the entry and treatmentresponse criteria described in our article.1 Their finding, in contrast to ours, was that haloperidol did not differentially affect pHVA in responders and nonresponders to haloperidol treatment.
Although their results appear to contradict findings from others and from our group,2 their study was limited in several methodologic respects. First, their minimum drugfree period was 3 days for oral medication and 1 month for depot neuroleptic treatment. It is therefore quite conceivable that baseline pHVA levels were still suppressed by previous neuroleptic treatment. Second, only one weekly pHV sample was taken instead of the two samples per week in our study.