The purpose of this study was to investigate the effect of using optical-scan sheets on the response rate in a mail survey. No empirical data were available on this question, but casual observation had indicated that many researchers are concerned about possible negative effects of using optical-scan sheets. Questionnaires of two lengths and two answer formats were used. The total random sample of 200 public school teachers was randomly divided into four groups: short or long questionnaire with op-scan sheet for recording responses; short or long questionnaire with instructions to answer directly on the instrument itself. The results indicate that there were no significant differences in response rate for groups using the optical-scan sheets and those answering on the questionnaire or for the groups receiving questionnaires of different lengths. Furthermore, there was no significant interaction between length of questionnaire and answer format. It was concluded that researchers may have the convenience of optical-scan sheets without any negative effects on response rate. (Author)