In this letter to the editor, the author discusses the idea that a paradoxical, or at least a biphasic, pattern or response may be characteristic of fluoxetine in particular, & perhaps of serotonergic drugs in general. He states that unpredictable responses, such as suicidal ideation or behaviours, may in fact be a predictable characteristic of drugs like fluoxetine which exercise their effects at all of the serotonin receptor subgroups. (15 refs.)