Alzheimer's disease is characterized by a slow, progressive decline in cognitive function and behaviour. Acetylcholine esterase inhibitors are the only agents approved by the Food and Drug Administration for the treatment of Alzheimer's disease. All other agents prescribed for the treatment of Alzheimer's disease are used on an off-label basis. Current research into new drugs is focused on agents that will prevent, slow down and/or halt the progress of the disease process. Salvia officinalis has been used in herbal medicine for many centuries. It has been suggested, on the basis of traditional medicine, its in vitro cholinergic binding properties and modulation of mood and cognitive performance in humans, that Salvia officinalis might potentially provide a novel natural treatment for Alzheimer's disease. The objective of this study was to assess the efficacy and safety of Salvia officinalis extract using a fixed dose (60 drops/day), in patients with mild to moderate Alzheimer's disease, over a 4-month period. This was a 4-month, parallel group, placebo-controlled trial undertaken in three centres in Tehran, Iran. Patients with mild to moderate Alzheimer's disease aged between 65 and 80 years (n = 42, 18 women) with a score of > or = 12 on the cognitive subscale of Alzheimer's Disease Assessment Scale (ADAS-cog) and < or = 2 on the Clinical Dementia Rating (CDR) were randomized to placebo or fixed dose of S. officinalis extract. Over the 16 weeks, the main efficacy measures were the change in the ADAS-cog and CDR-Sum of Boxes scores compared with baseline. In addition, side-effects were systematically recorded throughout the study using a checklist. At 4 months, S. officinalis extract produced a significant better outcome on cognitive functions than placebo (ADAS-cog: F = 4.77, d.f. = 1, P = 0.03) (CDR-SB: F = 10.84, d.f. = 1, P < 0.003). There were no significant differences in the two groups in terms of observed side-effects except agitation that appears to be more frequent in the placebo group (P = 0.09). The results of this study indicate the efficacy of S. officinalis extract in the management of mild to moderate Alzheimer's disease. Moreover, S. officinalis may well reduce agitation of patients but this needs to be confirmed.