In an attempt to evaluate the efficacy of different methods of interventions to improve the appropriate use of drugs for acute diarrhoea, a controlled study has been carried out in 6 districts in Yogyakarta and Central Java provinces, Indonesia. This study was designed to investigate the impacts of two different methods of educational intervention, i.e. a small group face-to-face intervention and a formal seminar for prescribers, on prescribing practice in acute diarrhoea. The districts were randomly assigned into 3 groups and 15 health centers were selected from each district. Prescribers in Group 1 underwent a small group face-to-face intervention conducted in the respective health center. Those in Group 2 attended a formal seminar conducted at the district level. Prescribers in Group 3 served as the control group. Both interventions were given on a single occasion without follow-up supervision or monitoring. Written information materials on the appropriate management of acute diarrhoea were developed and were provided to all prescribers in the intervention groups. Focus group discussions (FGDs) involving prescribers and consumers in the 6 districts were carried out to identify various underlying motivations of drug use in acute diarrhoea. The findings of the FGDs were used as part of the intervention materials. To evaluate the impacts of these interventions on prescribing practice, a prescribing survey for patients under five years old with acute diarrhoea was carried out in health centers covering 3-month periods before and after the intervention. The results showed that both interventions were equally effective in improving the levels of knowledge of prescribers about the appropriate management of acute diarrhoea. They were also partially effective in improving the appropriate use of drugs, reducing the use of non-rehydration medications. There was a highly significant reduction of antimicrobial usage either after small-group face-to-face intervention (77.4 +/- 2.7% to 60.4 +/- 2.9%; P < 0.001) or formal seminar (82.3 +/- 3.0% to 72.3 +/- 3.6%; P < 0.001), and the former caused significantly (P < 0.001) greater reduction than the latter. There was also a significant (P < 0.01) reduction in the usage of antidiarrhoeals after both interventions, i.e. from 20.3 +/- 3.7% to 12.5 +/- 3.3% (P < 0.01) after face-to-face intervention and from 48.5 +/- 4.1% to 27.0 +/- 4.3% (P < 0.01) after seminar. However, the formal seminar had a significantly (P < 0.01) greater impact than the small group face-to-face intervention. There was also a trend toward increased oral rehydration solution (ORS) usage after both interventions, but this did not achieve the level of statistical significance (P > 0.05). No changes were observed in the control group. Although the small group face-to-face intervention did not appear to offer greater impacts over large seminars in improving the appropriate use of drugs in acute diarrhoea, since the unit cost of training is far less costly than the seminar, it might be feasibly implemented in the existing supervisory structure of the health system.