Phosphatidylserine (PS) is a phospholipid which has been claimed to enhance neuronal membrane function, and can be derived from several sources. Earlier studies used brain cortex derived PS, of which the human tolerability of 300mg daily in 130 patients has been shown. The human tolerability of PS derived from soybean has not been reported, although it is widely sold as a nutritional supplement which may improve cognitive function in the elderly. We report the results of a study of the safety of two dosages of soy-phosphatidylserine (S-PS) in elderly. Subjects were 120 elderly of both sexes who fulfilled the more stringent criteria for age-associated memory impairment; some also fulfilled the criteria for age-associated cognitive decline. Subjects were allocated at random to one of the three treatment groups: placebo, 300 or 600 mg S-PS daily. Standard biochemical and hematological safety parameters, blood pressure, heart rate and adverse events were assessed at baseline, after 6 and 12 weeks of treatment. No significant differences were found in any of the outcome variables between the treatment groups after Bonferonni-Holme correction. In conclusion, soy derived PS is a safe nutritional supplement for older persons if taken up to a dosage of 200 mg three times daily.