INTRODUCTION The FORTRAN computer program presented in this Item may be used to determine the response of two-degree-of-freedom systems 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 modes of response are found. For second-order (oscillatory) modes the natural frequency@ damping ratio@ period and time to half-amplitude are found and for first-order modes only the time to half-amplitude is found. The dependent variables of the system are then found for the specified input forcing function(s) using a step-by-step integration routine.