Piecewise cubic polynomial spline interpolation [3] or smoothing [4] often gives undesirable inflexion points. We describe a spline interpolation method that allows to avoid these inflexion points and contains cubic splines as special case. The method is a generalization of the work in [2]. The proof of the theorem motivating the use of exponential splines is simplified. An ALGOL procedure is presented that allows to mix piecewise cubic and exponential spline interpolation suitably.