Mianserin seems to have little effect on peripheral noradrenaline (NA) re-uptake mechanisms as shown by its lack of effects on the tyramine dose and NA dose/pressor response. 2. Mianserin has no effect on the hypotensive action of bethanidine. 3. Mianserin in vivo has a significant action on platlet transport (Vmax) of 5-hydroxytryptamine (5-HT), which changes toward normal values in depressive patients on the drug. This action is not observed in vitro. 4. It is possible that a metabolite of mianserin is responsible for this effect, and that this may be of therapeutic importance.