This study described parent participation in the informed consent conference for randomized clinical trials (RCTs) in childhood leukemia and documented the relationship of physician communication to parent participation. Parents of 140 children with newly diagnosed leukemia who were eligible for RCTs were studied at six sites using comprehensive methods involving direct observation and transcripts of parent-physician communication based on audiotapes. Parent participation during the informed consent conference reflected a wide range of content categories. Consistent with hypotheses, Physician Rapport and Partnership Building related to parent participation in the informed consent conference but Information Giving did not. Higher parent socioeconomic status also was related to greater parent participation for two of three measures of parent participation. Findings suggest that physician behaviors that provide support and facilitate communication may enhance parental participation in the informed consent conference for RCTs in childhood leukemia.