Possible effects of the introduction of a new, experimental day-treatment programme combined with extramural and community care, as an alternative to standard inpatient treatment are studied over a period of three years (1986-1988) on the level of the regional mental health system. A psychiatric case register has been used to test hypotheses regarding changes in the patterns of admissions, of agents for referral, and discharge in the `substitution area' compared to nearby regions. No substantial effects with respect to these patterns were found. It might have been that the new approach has prevented a further increase of number of admissions which did occur in the other regions and also in the country as a whole.