The CCPC 90 conference and workshop included presentations by basic scientists describing the key in vitro and in vivo model systems used to study epithelial carcinogenesis and its associated biochemical and molecular alterations. A major conference theme was the identification of markers identifying specific carcinogenic stages. Current work focuses on defining the biology of preneoplasia, the critical specific molecular events in multistep carcinogenesis, and the dynamic interplay between viral, behavioral, dietary, and genetic factors in human carcinogenesis. Studies of molecular epidemiology and genetic susceptibility are identifying new risk groups and contributing to preventive strategies. Another major theme of the conference was the concept of field carcinogenesis and the study of carcinogen-exposed tissue "at risk" for the development of cancer. A specific example discussed by several investigators was the issue of SPT development in head and neck and lung cancers. Novel studies of biologic markers for use in early detection and as intermediate end points were described. The latter application, if validated in human trials, may allow short-term screening of chemopreventive agents and determinations of optimal doses/schedules for phase III chemoprevention trials. These biomarker trials may serve as a bridge between preclinical work and full-scale randomized trials. The status of the major phase III clinical trials was presented. Major problems in chemoprevention trials include (1) selection of agents, doses, and schedules, (2) lack of pharmacologic and pharma quality control, (5) adherence (drop-out and drop-in), and (6) trial-specific feasibility/recruitment, issues.