The effects of the chronic administration of the sigma ligand JO 1784 (igmesine) CRF-induced changes in some behavioural, immune, endocrine and neurotransmitter parameters were studied. In the elevated plus maze, CRF (1.0 µg i.c.v. daily × 5 days) induced a reduction in the number of entries and time spent on the open arms was significantly attenuated by the sigma ligand JO 1784 (3 mg/kg × 21 days) treatment. In the ‘open field’ apparatus, the CRF-induced increase in the locomotor activity was also reduced by JO 1784 administration. JO 1784 treatment did not alter the concentration of the biogenic amine transmitters in the hypothalamus, nor reverse the increase in the turnover of serotonin and dopamine caused by CRF. JO 1784 treatment also failed to reverse a CRF-induced increase in the serum corticosterone, but it did reverse the reduction in phytohaemagglutinin and concanavalin A-induced lymphocyte proliferation caused by CRF but not the changes in the lymphocyte and neutrophil numbers caused by the peptide. These results demonstrate that JO 1784 has some antistress properties in CRF-treate