Fecal concentrations of calprotectin were examined in 22 patients with Alzheimer's disease (AD) and compared with serum concentrations of aromatic amino acids. Calprotectin concentrations were mean ± SEM 140 ± 31.9 mg/kg, 16 patients (73%) presented with concentrations outside normal (>50 mg/kg). Concentrations correlated inversely with serum levels of tryptophan, tyrosine and phenylalanine (all p < 0.05). Increased concentrations of fecal calprotectin indicate a disturbed intestinal barrier function in AD patients which could be of relevance for the lowering of essential aromatic amino acids concentrations in the blood.