The effects of questions which differ in form and length on completeness and accuracy of information reported in household interviews were explored in a series of four field studies. Question length and structure were varied systematically while keeping constant the demand characteristics. Questions differed also in the recall time offered and the amount of redundancy contained. The analyses were based on tape-recorded interviews containing questions on health events and behaviors. The longer questions elicited more information than short ones. Indications are that the data were also more accurate. Several hypotheses are offered to explain these effects.