This study was an outpatient, randomized, double-blind, placebo-controlled trial of a combination amino acid formula (Gabadone) in patients with sleep disorders. Eighteen patients with sleep disorders were randomized to either placebo or active treatment group. Sleep latency and duration of sleep were measured by daily questionnaires. Sleep quality was measured using a visual analog scale. Autonomic nervous system function was measured by heart rate variability analysis using 24-hour electrocardiographic recordings. In the active group, the baseline time to fall asleep was 32.3 minutes, which was reduced to 19.1 after Gabadone administration (P = 0.01, n = 9). In the placebo group, the baseline latency time was 34.8 minutes compared with 33.1 minutes after placebo (P = nonsignificant, n = 9). The difference was statistically significant (P = 0.02). In the active group, the baseline duration of sleep was 5.0 hours (mean), whereas after Gabadone, the duration of sleep increased to 6.83 (P = 0.01, n = 9). In the placebo group, the baseline sleep duration was 7.17 +/- 7.6 compared with 7.11 +/- 3.67 after placebo (P = nonsignificant, n = 9). The difference between the active and placebo groups was significant (P = 0.01). Ease of falling asleep, awakenings, and am grogginess improved. Objective measurement of parasympathetic function as measured by 24-hour heart rate variability improved in the active group compared with placebo. An amino acid preparation containing both GABA and 5-hydroxytryptophan reduced time to fall asleep, decreased sleep latency, increased the duration of sleep, and improved quality of sleep.