Studies of the dynamic response of structures to wave-induced forces are presented. The objective has been to assess the effects and relative importance of some of the factors that affect the response and to evaluate the sensitivity of the response to some of these factors. The structures are modeled as viscously damped single-degree-of-freedom systems, and the wave forces are defined by Morison's equation using a Pierson-Moskowitz wave spectrum and linear wave theory to generate the fluid kinematics. Only responses within the linearly elastic range of deformation are investigated. A simpler excitation, composed of a sequence of a few pulses only, also is considered, and its effects are compared with those obtained for the more realistic representation of the wave loading. The responses of the systems are evaluated over a broad range of conditions, and the practical significance of the results are discussed. The factors investigated include the natural frequency and damping of the structure, the relative magnitudes of the inertia and drag components of the wave forces, the initial conditions of the forcing function and the structure, the phase angles involved in the definition of the fluid kinematics, the degree of periodicity of the wave excitation, and the degree of coupling or interaction between the oscillating fluid and the structure. The results are displayed in the form of response spectra.