OTENTIAL sources of bias in survey research are numerous. Phillips (1971: 12-49), for example, has listed anywhere from 13 to 18 different sources of potential bias in survey research and suggests that a substantial proportion of the findings resulting from such methods are probably invalid. Of the many sources that can contribute to bias in social surveys, two which lend themselves to examination by mail survey are setting and anonymity (or its lack): these are the focus of the present study.In arguing that setting alone can produce bias, Phillips (1971:33-34) cites the early work of Maslow and Mintz, whose results (Maslow and Mintz, 1956;Mintz, 1956) showed that rating of facial photographs by subjects varied according to the "esthetic" nature of the room in which the rating took place. In more recent work, Alutto (1970) found that businessmen were more likely to complete open-ended items on a questionnaire mailed to their office than one mailed to their home. In most studies, however, setting is seen as part of the more general defining aspects of the overall situation resulting in particular types of role enactment (see Abstract Anonymity was tested by placing an identifying number on half of the questionnaires on a mail survey designed to elicit reactions from teachers concerning teacher unions. Bias due to social setting was tested by mailing half the questionnaires to teachers at their home addresses, the other half to teachers at their school addresses. In a two-by-two factorial design, anonymity and social setting had no appreciable effect on response or speed of return, although social setting did have an effect on return rate. Respondents receiving the questionnaire at their school address had a higher return rate than those receiving it at home.