Three survey modes--a self-administered mailed questionnaire, a telephone interview, and a home interview--were assessed for survey costs, adequacy of completion, test-retest reliability, validity of responses to medical questions and estimates of morbidity. Costs per household for each mode were $A42.75, $A74.33, and $71.89, respectively. Item omission was confined virtually to the mail mode and averaged 5.5% over 84 questions assessed, while telephone and home interview modes averaged 0.4% and 0.2%, respectively. "Don't knows" were virtually absent for all questions except those about precise details (names, places, etc.) of events occurring often 10-15 years before the survey; no mode differences were observed. The mail mode produced less reliable responses to questions about environmental exposure to hazardous chemicals or activities when considered question-by-question, but differences were not significant among modes when all questions were grouped. Reliability was high to medical questions and no mode differences were observed. Medical conditions which would require a medical diagnosis for subjects to be able to report them were more reliably answered than conditions described in broad or lay terms. Validity of answers to medical questions varied across modes and types of questions; underreporting of medical conditions was highest in the mail mode and was lowest for conditions requiring a diagnosis. Overreporting was lowest in the mail mode and highest for conditions requiring a diagnostic opinion.