The Data Item provides a Fortran program for the determination of the response of two-degree-of-freedom systems with constant coefficients to any known applied forcing functions. The program is capable of dealing with any two-degree-of-freedom system the description of which requires two independent coordinates and which can be described by two second-order constant coefficient differential equations. The independent coordinates are the dependent variables of the system. An applied input forcing function is allowed for each second-order equation and to ease program input one of six possible types of input function can be specified: zero@ impulsive@ step@ cosine@ sine and an arbitrary input. The program evaluates the characteristic polynomial of the system together with the roots of this equation from which the natural frequencies and damping ratios and/or first-order time constants of the modes of the system are found. The dependent variables of the system and their first and second derivatives are then found for the specified input forcing function(s) using a step-by-step integration routine.