In traditional Chinese medicine a mixture of bee pollen, radix polygoni multiflore, semen ziziphi spinosae, radix salviae multiorhizae, fructus schisandrae and fructus ligustris lucidae, known as NaO Li Su, has a reputation as a remedy against declining memory functions. In the present study the effect of the preparation on failing memory was assessed in 100 elderly Danish volunteers who complained of a deteriorating memory. The study was a double-blind placebo controlled cross-over trial. The effect was evaluated after treatment periods of 3 months' duration by a battery of psychological and biochemical tests. No desirable effects on memory functions were achieved by the active treatment. Increases in the number of red blood cells and in the serum creatinine levels were seen after active treatment. In the subgroup initially showing a number of red blood cells below the median a significant positive correlation was found between changes in the number of red blood cells and changes in the Wechsler Memory Scale scores.