The treatment of patients who are dependent on opiates has definitely been including drug substitution besides withdrawal and weaning in the Swiss urban community ("Kanton") of Basel City since 1980. After a significant increase of treatments in 1987 in connection with the spread of HIV infections, more than 800 patients were presently receiving substitution treatment according to a descentralised schedule. The type of long-term treatment is illustrated by sociodemographic and treatment data of 500 substituted individuals who are mostly being looked after always by the same persons entrusted with caring for them. This represents a flexible, economically feasible and highly individual type of care and treatment that can help to reduce illegal drug consumption and hence the undesirable events associated with it in an urban district such as Basel city.