The objective of this study was to confirm whether the combination of a health education programme with a mass treatment campaign was able to improve the effectiveness of trachoma control. An open controlled clinical trial with a 2 x 2 factorial design was carried out. Four villages, matched for size and epidemiological, economic and social conditions, were included in the study. The first village received mass treatment with 1% oxytetracycline eye drops combined with a specific health education programme. The second village received only a health education programme. The third village received only mass treatment and the fourth village did not receive any intervention during the study (control village). 1810 subjects were enrolled of whom 76% were successfully followed for 6 months. The incidence of new cases ranged between 1.6% and 14.2%. In this study the combination of a health education programme with mass treatment failed to increase the cure rate. There was even a negative interaction (P = 0.03). The best results were obtained in the village where antibiotic treatment was used alone, both in terms of cure rate (82%) and reduction of C trachomatis transmission. These results suggest that the addition of a health education programme does not systematically improve the performances of a mass treatment campaign. The efficacy of this combination depends essentially on the capacity of the community to modify its hygiene behaviour.