5'-Methyltetrahydrofolic acid (5'-MTHF) in addition to standard psychotropic medication significantly improved clinical recovery in depressed patients with borderline or definite folate deficiency, and significantly reduced depressive symptoms in elderly normofolatemic patients after 3 weeks of treatment. In this equivalence study the effect of 5'-MTHF on depressive symptoms and cognitive status was compared to Trazodone (TRZ) in normofolatemic elderly patients with mild to moderate dementia and depression. Ninety-six patients with dementia, scoring 12-23 at the Mini Mental State Examination (MMSE) and > or = 18 at the Hamilton Depression Rating Scale (HDRS) after a 2-week placebo run-in, were randomized to receive either 5'-MTHF (50 mg/day p.o.) (47 patients) or TRZ (100 mg/day p.o.) (49 patients) in a double-blind design for 8 weeks. HDRS was assessed before, after 4 weeks and at the end of treatment; Rey's Verbal Memory (RVM) test for immediate and delayed recall was evaluated before and after treatment. After 4 weeks of treatment HDRS score was reduced from 23 +/- 5 to 20 +/- 6 in the 5'-MTHF (p < 0.05 vs baseline), and from 23 +/- 3 to 21 +/- 4 in the TRZ group (p < 0.05 vs baseline). A further significant decrease to 18 +/- 6 and 19 +/- 5 respectively was obtained at the end of the treatment period (p < 0.05 vs week 4) with 5'-MTHF and TRZ.(ABSTRACT TRUNCATED AT 250 WORDS)