The effect of AHN 086 [1-(2-isothiocyanatoethyl)-7-chloro-1,3-dihydro-5-(4- chloro-phenyl)-2H-1,4-benzodiazepine-2-one hydrochloride], an irreversible ligand of the mitochondrial benzodiazepine receptor, was studied in the heat shock protein (HSP) expression and the activation of dog neutrophils. At micromolar concentrations, AHN 086 induced a dose-dependent increase in free radical production (309 +/- 13% at 1 x 10(-5) M). This compound also increased the phagocytic activity (73 +/- 3.5% at 5 x 10(-6) M). Immunohistochemical results showed that AHN 086 induced the expression of HSP in neutrophil membranes. At 1 x 10(-5) M, the percentage of positive cells was: 90.2 (27 kD), 90.6 (72 kD) and 92.8 (90 kD). This expression was accompanied by a decrease in the presence of nuclear and cytoplasmic HSP. Flow cytometry studies showed that this cell membrane expression was located on the neutrophil surface and could be a consequence of HSP mobilization from nucleus and cytoplasm.