Reciprocity is fundamental to effective mentoring relationships. However, we argue that it is inappropriate, and perhaps unethical, to expect comparable levels of reciprocity in all mentoring relationships. Instead, contextual factors influence optimal levels of reciprocity. Foremost is the developmental stage of the protege, with less mature, relatively inexperienced proteges generally less capable of forming and maintaining a reciprocal relationship with their mentors than are more mature, relatively experienced proteges. We discuss three examples of contextual variables that can affect appropriate levels of reciprocity--the academic research apprenticeship, gender, and culture--and argue that mentors' expectations of reciprocity necessarily must be adjusted in order to achieve ethical mentoring within these contexts.