Animal and human studies have indicated that viloxazine hydrochloride, an antidepressant drug with a half-life of 3-4 h in most subjects at low dosage, is rapidly and almost completely absorbed after oral administration. A sustained-release form might be useful to decrease the frequency of administration. In our study, the pharmacokinetics of sustained-release form containing 300 mg viloxazine were compared with 300 mg conventional viloxazine in 11 normal volunteers (6 women, 5 men). Wide interindividual variations were observed with respect to plasma levels, but there was no significant statistical correlation between weight and blood concentration (conventional form: Cmax = 3,599 +/- 579 ng/ml, tmax = 86 +/- 26 min; sustained-release form: Cmax = 1,917 +/- 922 ng/ml, tmax = 215 +/- 77 min). Twelve hours after administration, plasma levels ranged between 540 and 1,600 ng/ml for the conventional form and between 660 and 2,120 ng/ml for the sustained-release form. Despite the great interindividual variation this new viloxazine form appears to be of interest for one daily administration.