Given a class $\mathcal G$ of graphs, probe $\mathcal G$ graphs are defined as follows. A graph $G$ is probe $\mathcal G$ if there exists a partition of its vertices into a set of probe vertices and a stable set of nonprobe vertices in such a way that non-edges of $G$, whose endpoints are nonprobe vertices, can be added so that the resulting graph belongs to $\mathcal G$. We investigate probe 2-clique graphs and probe diamond-free graphs. For probe 2-clique graphs, we present a polynomial-time recognition algorithm. Probe diamond-free graphs are characterized by minimal forbidden induced subgraphs. As a by-product, it is proved that the class of probe block graphs is the intersection between the classes of chordal graphs and probe diamond-free graphs.