As part of a project "Music therapy in internal medicine" we investigated 32 consecutive patients undergoing gastroscopy for various reasons. Patients were randomly assigned to two groups, regardless of sex, age or underlying disease. One group listened to music during gastroscopy, while the other did not. The choice of the type of music within the corresponding group was made with the patient and a trained music therapist in a short discussion prior to gastroscopy. The hormones ACTH and cortisol, as well as the catecholamines adrenalin and noradrenaline, were measured in both groups with three blood samples taken before, directly after and one hour after gastroscopy. Parallel measurements included blood pressure and pulse rate as well as questions about the patients' feelings during gastroscopy. The study showed the rise in the plasma levels of the stress hormones ACTH and cortisol to be significantly lower under the influence of music. The subjective feelings of the patients concerning "fear in general" and "fear about gastroscopy" paralleled these findings. Conversely, the plasma adrenalin and noradrenaline levels before and after gastroscopy were virtually unchanged in both groups, as were pulse rate and blood pressure. This study shows the influence of music on human biochemical parameters when used in the setting of a diagnostic procedure.