Proceedings of a symposium organized in co-operation with the United States Nuclear Regulatory Commission and Battelle Columbus Laboratories, Columbus, Ohio, from 28 October to 1 November 1985. Five topics related to source term evaluation were selected for review and discussion, namely in-vessel release, retention in the primary circuit, ex-vessel release, retention in the containment and release from the plant. Contents: Opening session; In-vessel release; Retention in the primary circuit; Ex-vessel release; Retention in containment; Containment challenges (Panel A); Release from the plant; Regulatory implications (Panel B).