This paper describes an empirical study of mentor and mentee behaviors deemed critical for developing healthy mentoring relationships and effective mentoring during the "start up" and "on going" stages of a formal mentoring scheme within a major UK public sector organization. Several identified behavioral categories (criteria) of mentoring effectiveness provide significant support for Kram's (1985) two-function model of mentoring relationships and for various "best practice" models of effective mentor and good mentee behavior. (Contains 4 tables.)