Background: Xenotransplantation may eventually provide a solution to the worldwide shortage of human organs for transplantation. Xenotransplantation is surrounded by profound ethical issues, both for the potential recipients and for the society as a whole. Concurrent with increased scientific interest, there has been an increasing number of quantitative public opinion surveys conducted about xenotransplantation in the last decade. The aim of the present study was to elucidate these surveys, and to assess some factors that may affect the outcome of them. Materials and methods: Surveys were identified by web and literature searches using key words in Medline and ISI Web of Knowledge. Reference lists of identified surveys were checked. Data was obtained from Inter-University Consortium for Political and Social Research (ICPSR) and directly from authors whose data were presented in another way than percentages. In total, the present material covered surveys from 35 sources, including 23 countries. Results and discussion: Results showed that almost half of the respondents accept xenotransplantation, whereas the remaining half did either not accept or did not have/state an opinion. Over time, the proportions of acceptance seemed unchanged. The proportion of those who did not accept decreased and the remaining proportion increased. This pattern was evident in Europe and the US, but not in Japan. Gender and education were found to be associated with opinions to xenotransplantation. The influence of religion was not as straightforward. This may partly depend on how religiosity was measured in the polls. Wording of items influenced levels of acceptance. If a xenotransplant was the ''only choice'' proportions of acceptance increased, and if a ''risk for zoonotic diseases'' was stated proportions of acceptance decreased. When wording of survey items was somewhat comparable, there were often, but not always, minor differences in proportions of acceptance between surveys from different sources. Trends in opinions are best measured by the use of the same items. It is however difficult to phrase items that will not be affected by external events.
