For a given pseudo-Hermitian Hamiltonian of the standard form: H = p 2 /2m + v(x), we reduce the problem of finding the most general (pseudo-)metric operator η satisfying H † = ηHη −1 to the solution of a differential equation. If the configuration space is R, this is a Klein-Gordon equation with a nonconstant mass term. We obtain a general series solution of this equation that involves a pair of arbitrary functions. These characterize the arbitrariness in the choice of η. We apply our general results to calculate η for the PT -symmetric square well, an imaginary scattering potential, and a class of imaginary delta-function potentials. For the first two systems, our method reproduces the known results in a straightforward and extremely efficient manner. For all these systems we obtain the most general η up to second order terms in the coupling constants. PACS number: 03.65.-w Consider a physical system described by a separable Hilbert space H and a pseudo-Hermitian Hamiltonian operator H : H → H. Let M denote the set of all linear invertible Hermitian operators η : H → H, then by definition [14] the pseudo-Hermiticity of H means that M H := {η ∈ M|H † = η Hη −1 } is a nonempty subset of M. The elements of M are called pseudometric operators, for they may be used to define a pseudo-inner product (a nondegenerate sesquilinear form [15]) ·|· η := ·|η· on H, where ·|· denotes the defining inner product of 1 The same way Einstein's equation does not generally restrict the metric tensor to have a particular signature, the above-mentioned equation does not restrict its solutions to correspond to positive-definite metric operators.