Comprehension of informed consent materials from a study of psychological variables associated with chest pain was evaluated as a function of age (27 to 69 years), education (5 to 20 years), and readability of information [low (college level) versus high (7th grade)]. The potentially confounding effect of memory was eliminated by allowing patients to use the written information sheets to find answers to the multiple choice test. Feedback and a repeat test were provided if any answers were incorrect. The findings indicated that comprehension varied inversely with age and directly with education. It is suggested that while ensuring informed consent may be difficult for all volunteers, it may be a critical problem for elderly patients with low education. The effects of readability were not consistent, suggesting that simplifying informed consent materials by shortening words and sentences may not, by itself, be sufficient to improve comprehension.