Background: The effectiveness of voluntary reporting systems in pharmacovigilance highly depends on the number of assembled reports. Aim: The aim of this study was to measure the effect of the periodical distribution of a bulletin on drug safety issues and of including yellow cards in prescription pads on the rate of adverse drug reaction (ADR) reporting. Study Design and Methods: The Catalan Centre of Pharmacovigilance began its activities at the end of 1982. Since 1985, an ADR bulletin (ADRB) has been mailed approximately quarterly to all physicians in its catchment area, with one yellow card enclosed. Additionally, from 1991-1994, a yellow card was included in the prescription pads of the Catalan Health Service. Time series methodology, with adjustment of the monthly number of reports to an Auto-Regressive Integrated Moving Average (ARIMA) model, was used to evaluate the effect of these two measures. Results: From January 1983-October 1995, 6240 spontaneous ADR reports were received, and 41 issues of the ADRB were sent out. Initially, the mean monthly spontaneous ADR reporting rate was 34.4 (SD = 14.1; n = 106 months). After the inclusion of yellow cards in prescription pads, the mean monthly spontaneous ADR reporting rate increased to 53.9 (SD = 14.4; n = 48 months). According to an ARIMA model, when a bulletin was send out (MONTH1), a mean increase of 9.4 reports was produced in that month, plus 12.3 additional reports in the following month (MONTH2), and 6.3 in the second month after sending the ADRB (MONTH3). A yellow card in the prescription pads elicits a monthly mean increase of 19.8 in the number of reports. Conclusions: The present study suggests that ADRBs elicit a temporal increase of the ADR reporting rate. Including a yellow card in prescription pads was followed by an even greater increase in the reporting rate, possibly because it guarantees that yellow cards are available at the workplace.