Conversation analysts have noted that, in psychotherapy, formulations of the client's talk can be a vehicle for offering a psychological interpretation of the client's circumstances. But we notice that not all formulations in psychotherapy offer interpretations. We offer an analysis of formulations (both of the gist of the client's words and of their implications) that are diagnostic: that is, used by the professional to sharpen, clarify or refine the client's account and make it better able to provide what the professional needs to know about the client's history and symptoms. In doing so, these formulations also have the effect of shepherding the client's account towards subsequent therapeutic interpretation. In a coda, we notice that sometimes the formulations arc designed discreetly. We examine one such discreet formulation in detail, and show how its very ambiguity can lead to its failure as a diagnostic probe.