A placebo-controlled crossover design, with each treatment period lasting 6 weeks, was used to investigate effects of dronabinol in 15 patients with a diagnosis of probable Alzhemer's disease who were refusing food. Eleven patients completed both study periods; one patient who died of a heart attack 2 weeks before the end of the study was also included in the analysis. The study was terminated in 3 patients: one developed a grand mal seizure and 2 developed serious intercurrent infections. Body weight of study subjects increased more during the dronabinol treatment than during the placebo periods. Dronabinol treatment decreased severity of disturbed behavior and this effect persisted during the placebo period in patients who received dronabinol first. Adverse reactions observed more commonly during the dronabinol treatment than during placebo periods included euphoria, somnolence and tiredness, but did not require discontinuation of therapy. These results indicate that dronabinol is a promising novel therapeutic agent which may be useful not only for treatment of anorexia but also to improve disturbed behavior in patients with Alzheimer's disease.