A formal theory of two-step (p,2p) reactions was developed, based on a combination of the R-matrix theory of continuum states and the formal reaction theory appropriate to a direct (p,p') reaction with final-state distortion, The formal theory yields an expression for the angular correlation between the two protons emerging from a two-step process involving an isoIated intermediate state. This expression is obtained explicitiy for the simplest plane-waveBorn- approximation description of the (p,p') process. The effects of antisymmetric wave functions, neglected in the early pants of the paper, are discussed at the end in terms of the formal theory. (auth)