A double-blind parallel comparison of alaproclate and placebo was carried out in patients suffering from senile dementia of primary degenerative type, or multiinfarction dementia. Both groups consisted of 20 patients each, valid for efficacy evaluation. The patients received either alaproclate 200 mg twice daily or placebo according to a randomized procedure. The study started with a placebo washout period of 2 weeks followed by a 4-week period of active treatment or placebo and a finishing 2-week placebo washout period. The efficacy was evaluated with a dementia rating scale by Gottfries, Bråne and Steen (GBS), selected items from the Comprehensive Psychopathological Rating Scale (CPRS), a rating scale for dementia adapted for nurses, and by clinical global evaluations. No difference in efficacy between the two treatments was observed with the exception of the intellectual factor of the GBS scale, where a statistically significant improvement was detected in the alaproclate group compared with the placebo group. There were no serious adverse symptoms.