Against a background of falling revenues and increasing expectations, health care systems in central and eastern Europe are facing increasing budgetary gaps. There is extensive anecdotal evidence that these gaps are being filled by informal or 'under-the-table' payments. These are important because of their implications for estimates of future funding requirements, for equity, and for the possible perverse incentives they introduce for those providing and managing health services. There is, however, relatively little information on either their scale or how they are perceived in these countries. We report the results of a small survey from Bulgaria that begins to address these issues. Data were collected by means of an interviewer-administered household survey in which those who had used state-provided health services in the preceding 2 years were identified. The survey took place throughout Bulgaria in 1994. One thousand people were approached and 706 (70.6%) provided information suitable for analysis; 42.9% had paid for services that were officially free. Payments had been for a wide range of services and to differing groups, including medical, nursing and ancillary staff. Payments to individuals during consultations were between 3% and 14% of average monthly income but the average cost of an operation was 83% of mean monthly income. There were large differences in the amounts paid by individuals. Most people were in favour of both official user fees and health care reform, except among the old, the poor, and those in poor health. Despite certain limitations, this study gives some indication of the scale of informal payments in Bulgaria. Several possibilities exist to address them. Contrary to what is often argued, there seems to be a popular willingness for them to be converted into formal co-payments. Before this can be done, there is a need for more research on the impact that this would have on equity and affordability.