Human resources data (HRD) inputs often fail to influence system development. This study investigated the possibility that these inputs are sometimes deficient in quantity or timing. In addition, the effect upon design of different personnel quality and quantity requirements was analyzed. Equipment and HRD inputs which were produced during actual missile development were presented to eight design engineers, who were required to develop a conceptual design of the equipment. By varying personnel constraints and timing of inputs, the study found that the type of manpower requirement and the amount and timing of HRD inputs influence design, although somewhat unpredictably. The estimates of personnel required to operate and maintain systems does not always relate to design concepts. The study concluded that personnel requirements should be included in proposal requests and work statements and recommended that further research be undertaken to describe the design implications of HRD inputs. (BH)