Thirteen HIV positive schizophrenic patients (Group 1), age ranging from 23 to 60 years, diagnosed as schizophrenics (DSM IV), were studied during a four week hospitalization period, due to an acute exacerbation phase. The patients were treated with haloperidol(3-15 mg/die p. o.) and diazepam (2-25 mg/die p.o.). Clinical picture and side-effects were assessed by BPRS, HRS-A, HRS-D, and DOTES, at admission and after 2, 3, 4 weeks of hospitalization period (Time 5, 7, 8, 9). Clinical evaluations were compared to a previous hospitalization period, before seroconversion (Time 0, 2, 3, 4), and to a control group (Group 2) of HIV negative schizophrenic patients (11 pb) followed as well during 2 periods of hospitalization. Our data seem to emphasize that the HIV infection could induce organic alterations in the CNS which might cause psychopathological consequences : significatly more severe depressive symptomatology and a reduction of tolerability to neuroleptics in the seroconverted patients' group.