Optimal control of long-term sedation during therapy in the intensive care unit is difficult to achieve in a number of patients when based on commonly used clinical sedation scores alone. We therefore used the median frequency of the EEG power spectrum as a quantitative measure for closed-loop administration of propofol in 21 artificially ventilated patients (nine trauma, 12 non-trauma). The EEG setpoint was correlated with a clinical sedation score and defined such, that mechanical ventilation was tolerated. The sedative therapy was given for 31±30 h. Non-trauma patients required sedation with an EEG median frequency between 2 and 3 Hz (propofol consumption: 1.4±0.8 mg kg−1 H−1) and sedation seemed to follow some circadian patterns, whereas trauma patients needed significantly deeper sedation (EEG median frequency: 1–2 Hz; propofol consumption: 2.6±0.8 mg kg−1 h−1). We conclude that the EEG closed-loop system could safely and reliably administer propofol to maintain a predetermined level of sedation for patients in intensive care unit over a protracted time.