This clinical study was conducted to evaluate the tolerability and efficacy of a new galenic formulation of a herbal sleeping aid, a valerian/lemon balm combination, to treat minor sleep disorders. The study was performed according to a randomised, placebo-controlled, double-blind, parallel group, multicentre design with healthy volunteers. Primary parameters were the assessment of the overall tolerability and the incidence of adverse events. Secondary parameters included laboratory tests, physical examination and assessments of well-being and sleep quality. The preparation proved to be well tolerated by most subjects (93% of the participants in the valerian/lemon balm group and 91% in the placebo group). There was no statistically significant difference concerning the frequency of adverse events between the two treatment groups (vaierian/lemon balm 29%, placebo 28%) and no serious adverse events were reported, No significant changes were seen in regard to laboratory tests, physical examination and rating of well-being. In contrast, the valerian/lemon balm group revealed a significantly higher quality of sleep (33%) compared to the placebo group (9%), P-value = 0.04. In conclusion, these results indicate that this valerian/lemon balm formulation is well tolerated. (C) 1999 Elsevier Science B.V. All rights reserved.