We explore the relationship between R. W. Shephard's input distance function (``Cost and Production Functions,'' Princeton Univ. Press, Princeton, 1953) and D. G. Luenberger's benefit function (J. Math. Econ. 21 (1992a), 461 481). We point out that the latter can be recognized in a production context as a directional input distance function which can exhaustively characterize technologies in bo...