In a field, such as drug use in pregnancy, where knowledge is often based on scanty information, and systematic permanent surveillance is needed, so as to avoid reliance on data obtained in widely differing contexts, an international co-operative network was set up, using a cheap and standardized interview technique. The study, originally European, can now be considered 'intercontinental', as the twenty-five countries where data is already being collected represent four of the five continents. Thirteen participating countries have already returned about ten thousand completed forms. Fifteen per cent of the 9714 enrolled women took no drugs at any state of pregnancy, while each taker received an average of 2.6 (range 1-13) prescriptions. Intracountry and intercountry differences were found in prescribing habits and in other characteristics of the population. Although the large amount of data collected is still being processed, preliminary findings indicate that this study seems to have been warranted.